Bitcoin Forum

I've curious lately to know about "Transaction Finality" on the Bitcoin blockchain. Even after being years on the crypto space, there are a lot of things related to Bitcoin's technical aspects which I'm not aware of. I'd like to know how many confirmations does a transaction need to be considered as "final" on the Bitcoin blockchain?

This is important, because if Bitcoin lacks transaction finality, then a few forks here and there could alter the history of your transactions across the Blockchain. Ethereum has been deeply concerned about "Transaction Finality" which is why the dev team has come up with Casper PoS + Sharding consensus to prevent this. Does this mean that transactions on a PoW blockchain are not final at all? I'm sort of confused with this, and I'd like someone to help me clarify about this matter.

Any help would be greatly appreciated. Thanks in advance. :)

In short, there's no such concept.

As far as I know, confirmations are different from finality in a blockchain. Confirmation is the amount of validation made my miners on a transaction. On the other hand, Finality refers to the method on how blockchain protocols consider a transaction final.

On Bitcoin network, they appeal on what's called Probabilistic Finality. From the term itself 'Probability', it appeals to the chances of reverting a transaction to mere impossible, because it digs deep the transaction of up to six blocks, making forks extremely difficult to alter hashes.

There are other types of finalities for other blockchain-based systems. Though all of them are given criteria for either availability (fast transactions), or consistency (security filtering out bad transactions).

Reference here: https://medium.com/mechanism-labs/finality-in-blockchain-consensus-d1f83c120a9a

Most exchanges consider 3 confirmations secure enough to consider a transaction as final. This website uses 6 confirmation as an example but it perfectly shows how secure the Bitcoin network is, compared to altcoins: https://howmanyconfs.com/

I think most exchange consider 1 transaction on Bitcoin Blockchain to be consider as final. The same is applicable for wallets as after 1 confirmation you can retransfer Bitcoin to another wallet. Actually 10 confirmation are required but, 6 is considered final.

we define a transaction to be "final" when it has a certain number of confirmation so that the cost of reversing it is so huge that it can be considered piratically impossible.
in bitcoin, 1 confirmation already increases the cost of reversing it (the 51% attack) by a lot but usually 3 is the magic number of confirmation that you can call it "final". of course there are additional consideration such as the network state, for example if there is a planned fork like in 2017 that could have a risk of splitting the chain. and also the type of node the user is running (full versus SPV).

it comes down to how centralized the cryptocurrency is. for example in bitcoin thanks to its decentralization you can't just have a fork anytime you want! forks take a lot of  time and convincing of the entire network (or at least 95% of them) to take place otherwise they won't happen. in short you have to ask whether the cryptocurrency is immutable or not.
but when it is centralized, has low hashrate, has flaws in the protocol,... like ethereum, new attack surfaces exist that can increase risks. we saw how the ethereum owners easily reversed a huge number of blocks a couple of years ago, which led to ETH not being immutable anymore. and that means your ethereum transactions can never be considered final no matter what.

It would depend on the transaction amount in my opinion. For small transactions in the Bitcoin blockchain, one is usually enough, for bigger, some merchants ask for three, some for six confirmations.

Plus also because of the total hashing power that Bitcoin has, one confirmation is equal to more confirmations in other blockchains, which make the other blockchains less secure.

"A few forks here and there."Haha,that's funny.
Can you explain in detail how a few forks can alter our transaction history?You admit that you are not an expert in Bitcoin's technical aspects,but you question the security of the blockchain and you come up with this weird "transaction finality" concept.
I'm not a blockchain guru or expert,but I have my own childish and oversimplified concept about how the blockchain works.
Old transactions get confirmed again and again every time a new transaction happens.The new transactions get confirmed again and again,every time a newer transaction happens.That's why we call it blockchain.It's like a chain. ;D

Is this related to exchange or wallet? 10, 6, 3, or whatever number it is, most of them are self-decided by the exchanges.

The number of 'required' confirmation is 'arbitrary'. Considering how secure the network right now then 1 confirmation is probably good enough for most cases.

Bitcoin's blockchain records basically the money flow. It doesn't care about the actual wallet and how "final" you feel the funds in it are.

This being said, all you know is if an input has "enough" (which can have various meanings) number of confirmations and you can or cannot spend it (it's yours or not). That's just simply all.

Exactly. The more confirmations a transaction has, the lesser the probability of "rollbacks" will be. Since Bitcoin is the most secure Blockchain network today, a single confirmation might be all you need to feel safe without worrying about getting your funds "double-spent". The real deal will be with smaller blockchain networks which are easily prone to a 51% attack. Maybe the Ethereum developer team have been concerned about transaction finality because of security issues within the chain? After all, Ethereum is not as secure as Bitcoin is in terms of hashrate.

One thing for sure, is that transactions made on PoW blockchains are considered as "final" while that's not the case with PoS blockchains (someone correct me if I'm wrong). The amount of energy spent mining Bitcoin compensates for the security and reliability of the entire Blockchain network. It could be said that transactions on the Bitcoin blockchain are considered as final after a couple of network confirmations. But no one knows for sure, as Blockchain technology is still being thoroughly tested within the mainstream world. Just my thoughts ;D

It depends on the system of the exchange to give exact figures. in fact it is just a number to confirm exactly which blocks of blocks have been received to process or not. exchanges usually only need 3-5 confirmations of completing a transaction and this is quite normal. When an error occurs, the blocks will surely stop processing and be canceled, then the system will notify that your transaction has failed and ask you to make a new transaction. Simply put, the blockchain system is quite smart and you don't need to worry too much about this.

it is not that complicated to know. it is a matter of cryptography. in order to reverse a transaction that is already confirmed you have to mine the same block. but the problem is that you have to first have a huge hashrate that allows you to mine that block within reasonable time. lets say it is block #100, while you are mining that again the rest of the world is mining #101 and by the time you find #100 the rest of the world is on #102 now you are 2 blocks behind and the chain you have is a shorter one with less work that is rejected.

The smaller coins have encountered 51% attack before and it was profitable for them due to the relatively lower cost of the attack as compared to the amount double spent. It is important to consider the number of confirmations required to the total value of the transaction. For the lower value transaction, it's possible for the transaction to be instantaneous if the merchant is willing to take the risk for the sake of a faster and smoother checkout. For exchange, they usually require a much higher number of confirmations. Up till 5 confirmations, the risk of double spending with less than 51% of the network is still possible (albeit still rather expensive and requires some luck).

I once too became curious about how many confirmation is needed in order to completely verify a transaction, and why does it needs to have more than 2 confirmation just to completely made a transaction successful. With this regard, I have came up to conclusion that the transaction is quite more secured based from the number of confirmation it gets from the miners.

Most of the time, the transactions I've created is already been processed with just at least 3 confirmation on the network.

I apologize for the concern, but I am concerned about one question, how vulnerable the transaction can be, until the first confirmation, since I used to consider the blockchain bitcoin flawless at all levels of its use.  Is it possible to cancel a transaction before the first confirmation in the bitcoin blockchain?  I understand that many blockchains and different coins have flaws and especially the facts of vulnerability, but there is nowhere to get information about the real possibilities of loss.

It's somewhat alright to accept zero-conf transactions if it ticks a few criteria. Generally, with opt-in RBF flag in the transaction, it is a very high risk transaction since the ease of double spending that transaction is extremely high; anyone can easily replace it with another transaction to an alternative address. In a brick-and-mortar store where the customer would want a fast transaction settlement, it would be more advisable to accept zero-conf transaction following a risk assessment.

Once it has one confirmation at least, it is generally safe to accept transaction of a decent value.

Ethereum is concerned with "transaction finality" because they want to switch to PoS, and in PoS 51% attacks are more dangerous because of the "nothing at stake" problem, which is why they try to invent some countermeasures to deal with this problem. Bitcoin is a PoW currency, so you don't have to worry about it as long as the hashrate remains big enough, and currently it's really big and keeps growing.

Newbies, Nothing at Stake is NOT a myth. It's a known theoretical weakness in POS. In POS, a bad actor will not lose anything if he/she misbehaves, by signing in each and every fork. In fact, it encourages them to sign each and every fork because there are no costs.

How this confirmation becomes arbitrary? I often got experience this when Im doing some transactions on different exchange. The confirmation varies and they have different figures such as Binance, Kucoin, and even wallet transactions. Is the exchange changing it or the blockchain securing this confirmation and validation or they just prefer it depends on the level of security that is being process?

Attack the debate, read my post and explain how the theory can't be put into practice? A need for a "multi-stake client"? Is that term your own invention? I believe so. ::)

On the topic of finality, POS requires/or WILL require checkpoints.

I still have a lot to learn about how "transaction finality" works on both consensus algorithms (PoW and PoS). For once, I've thought that the energy spent on PoW chains like Bitcoin and Ethereum, meant that transactions were considered as final (unlike PoS chains of today). Thankfully, you've helped me understand this better after some confusion related to the subject. I can now see why Ethereum is after "transaction finality" with its Casper PoS upgrade. Smart contracts need a truly immutable blockchain where transactions are considered as final no matter what. Those who try to cheat the system will get penalized. It's a clever idea from the ETH dev team, which could serve as a great example for Bitcoin and other altcoins.

While I don't like coded checkpoints because of their centralization, the latter option (rolling checkpoints) seem to be a better solution for maintaining transaction finality on the Bitcoin blockchain. I'm surprised that BTC devs are not interested in doing something like this, in order to make Bitcoin as immutable as possible. The current hashrate distribution on mining pools owned by Bitmain/China could put the blockchain at risk in the long term. After all, they already control 51% of the network's hashrate. There are solutions to tackle this problem, though. Betterhash, and Stratum V2 aim to make mining more decentralized. With a decentralized PoW consensus and rolling checkpoints, you could rest assured that Bitcoin's transaction history will remain unalterable for the foreseeable future.

But I guess that, developers are mostly interested in scaling the BTC blockchain than anything else. Of course, that's also important for the mainstream adoption of Bitcoin. But I believe that, security and reliability goes above anything else. As long as there's no threat of a 51% attack or block reorg, developers wouldn't care more or less implementing a mechanism that would make transactions final no matter what. :)



Yes. That's the way it works, according to the Bitcoin whitepaper. The longest running chain is the one that's considered as valid among all participants. We could say that Bitcoin experiences small forks every once in a while because of this. The situation is worse with PoW chains that have huge block sizes (like BCH and BSV). I've seen that Bitcoin SV has experienced a lot of block reorgs lately. In a chain like this, it's hard to think that transactions will ever be considered as "final". Maybe that's why BTC devs decided not to increase the block size in order to maintain Bitcoin as secure as possible. A 1mb block size has worked flawlessly for the Bitcoin blockchain where block reorgs have been quire rare (AFAIK). But I strongly believe that Bitcoin devs should look for ways to implement transaction finality on-chain to maintain the immutability of Bitcoin for the foreseeable future. :)

Is that all? That's the prevention of stakers from signing in each and every fork, at no costs? Good luck with POS finality. 8)


Zeit removed the fees? What are the incentives to stake, and to secure the network? That's not a network for a hostile environment.

to attack a network and put it to test there has to be incentives, when that network is garbage and the reward is so small that it doesn't even cover the cost of time spent looking into the garbage then it will never be attacked and it could create the illusion of being safe just because it hasn't been attacked.

Or their network is centralized to several stakers/validators who understand each other, that it's also not worth attacking. Buying up their cryptocurrency would be giving them a favor. Hahaha. 8)

OK, then we are back to the debate that stakers are incentivized to sign each, and every fork, because it costs them nothing. Plus if the only "challenge" to start doing it is modifying the software to enable signing each, and every fork, then good luck to finality in POS.

It's worth pointing out that we're giving someone ample opportunity to plug their coin, when such blatant advertising should be happening in the altcoin board.  If we're not going to steer the conversation back towards Bitcoin, I'd call for this topic to be locked/moved.

The question as to why Bitcoin no longer uses checkpoints is answered rather well here (https://bitcoin.stackexchange.com/questions/75733/why-does-bitcoin-no-longer-have-checkpoints).  I hope this clears up any confusion some people might be having.

The fact that nobody has done this doesn't mean that it can't be done. Right now there are couldwith such a weak PoW network that it would cost a few bucks to attack them with a 51% attack. See:https://www.crypto51.app/

Is anybody attacking them? Maybe. You and I don't care to even look into it most probably, but that doesn't mean it's not happening.
Is it feasible to attack them? Most certainly yes and it has been done in the past. Goldcoin (https://medium.com/@i.am.that.gullible/the-attacker-did-a-51-attack-on-the-goldcoin-blockchain-ffdca7413ed1) is a good example.

Theoretical attacks deserve as much attention, the fact that they remain in theory doesn't mean they aren't feasibe and that they don't pose as weaknesses of consensus algorithms.

The problem there is, I don't think you'll be able to convince me that they are wrong while you have such fundamental misconceptions over the supposed importance of checkpoints.  Your "detailed examples" are based on a flawed premise.  If you ever reach a better understanding of the matter, perhaps I'll reconsider.

Boy, there has been so much talk and work done to actually improve bitcoin's infrastructure that we could go on talking for ages. The man-hours of development done to improve bitcoin probably are more than the working hours you and I will both put out in our lifetimes. Bitcoiners DO take the theoretical attacks that could have been performed on bitcoin seriously. Maybe too seriously. To an extent that top developers put out extra effort to improve even marginal metrics of performance for bitcoin. At levels that further improvement requires expertise we'd have a hard time imagining.

Take bitcoin's network's infrastructure as an example. Sybil attacks, (which could aid in making the theoretical selfish mining attack more feasible), have become more likely because bitcoin devs managed to improve peering and propagation in the network, taking propagation down from dozens of seconds to a handful.

And this isn't a bitcoiner-altcoiner issue...  Advances in cryptocurerncy technology continue to be beneficial for the entire space. That's why we have to study even theoretical attacks carefully instead of being dismissive.

What you're presenting here is an appeal to authority (https://yourlogicalfallacyis.com/appeal-to-authority) logical fallacy (likely because you're fresh out of arguments).  Just because satoshi implemented a particular feature, it does not mean that feature can't be removed later if it no longer serves a purpose.  In the fledgling early years, checkpoints made sense, but as Bitcoin has evolved and grown, the decidedly limited protection they offer has simply made them redundant.  Bitcoin handles far too much wealth on a daily basis to revert back to an arbitrary earlier point in time.

I wouldn't claim to be smarter than satoshi, but I would proclaim you to be dumber than a box of rocks.

Exactly.  Which would be of zero consolation to anyone who received BTC after the checkpoint.  So, despite having literally just explained the primary weakness yourself, you somehow still can't see the problem?  

The troll could not accept a simple fact. That transaction finality is always in question in POS, because stakers are incentivized to sign in each, and every fork, because it costs NOTHING.

He will post nothing a lot of word-salad, with a lot of name-calling. 8)

Base on my research and the numbers of transaction confirmation most crypto exchange site usually require for transaction finality. I believe bitcoin transaction can be considered successful after 3 confirmation, ETH is 12-25 confirmations.


This kind of message is not welcome on this forum and i will advise you to be more careful next to avoid been penalize by the forum moderator.

i'm surprised that you still haven't put the Z shill on ignore, i keep seeing his comments in your quotes :P
in any case, if anyone thinks their beloved altcoin that they keep advertising is strong against attacks can put their money where their mouth is. put up a reward like half a bitcoin in a trusted escrow for anybody who pulls a successful attack on that altcoin and see how it fairs then...

I have the troll back on ignore. I thought he became reasonable. Haha.

Plus why would they put up a reward? They know POS is flawed. No expended energy, no costs, then dishonest activity that could take place, will take place. Lastly, it has no finality like Bitcoin's transaction finality.

As I understand, transactions are only as final as the network is secure.

The deeper a transaction is rooted in the blockchain, the more difficult it is to modify, since it would require more work to achieve.

This is because a large number of blocks would need to be undone by the attacker. Because of this, surface level blocks (e.g. ones that were just finalized) are more vulnerable to a majority attack, while a more sustained attack might be able to alter blocks from a few hours ago. Most platforms bank on the fact that such an attack would be thwarted well before older transactions are modified.

As I have known there are  three basics confirmations for most types of transactions , and of course they are enough for finishing any transfer of money. Fortunately, the confirmations does not last long especially when you put the appropriate value of fees. That is the advantage of Blockchain on  tranferts of banks, there is huge difference between them. Using Btc wallets will make your money  safe and secure and without exploitation  through the high value of taxes

the amount of the transaction confirmation fee will be by entering a very high nominal shipping fee, it will indeed make shipping fast but you should know that when the price of bitcoin rises, the exchange shipping fee will be expensive, bitcoin transactions will never be taxed, they only cut costs shipping for transaction fees from the central wallet.

One of the most substantial improvements today is with the use of bitcoin, and now many people getting more included in this world because they know the potential of this coin to make a lot of income for their investment. Also, many people would like to amend with the use of crypto as transaction fee because they know it is faster than the traditional way.

In terms of having security, it depends on the platform because most of the platforms today are using just only one verification, and after that, it is now completed. Only a few platforms are supporting the use of two-way authentication to make sure there is no problem in the transaction and also it is secured.

Exactly. That's the way it's been for PoW-based cryptocurrencies like Bitcoin and Ethereum. The real deal would be PoS-based cryptocurrencies with the "Nothing at Stake" problem. This would greatly undermine the transaction finality on PoS blockchain networks as validators/stakers will be able to support various forks without any costs involved. In PoW chains, it's much more difficult to revert transactions when they have a lot of confirmations on the network. The older the transaction is, the harder it'll be for anyone to "roll it back" within the Blockchain. In the case of ETH's DAO hack, it was easy to "roll back" transactions because they were relatively new/fresh. If time would've passed by without any action from the ETH community, it would've been near impossible to revert transactions on the Blockchain.

Nonetheless, I think that transactions on the Bitcoin blockchain are considered as "final" once they have a lot of confirmations on the network. The more confirmations, the more costly it'll be to perform a 51% attack in order to "roll back" transactions from the Blockchain. In my point of view, PoW provides better security against external attacks/manipulation than PoS itself. The decision of the ETH dev team switching from PoW to PoS could undermine the security of the Blockchain as we know it (even though it increases scalability/performance). I'd suggest that Ethereum and Bitcoin should adopt "checkpoints" in order to remain immutable for the foreseeable future. Just my thoughts ;D

We need to get back to the roots to solve this question... so let's start with why bitcoin needs confirmations? This is to avoid the double-spend problem... It is easy to double-spend a transaction without confirmations, but it's almost impossible to double-spend a transaction with 1 confirmation or more. For that, we need to make a 51% attack on the network, so. This is why with one confirmation we should feel secure but not safe.

Thanks for the clarification. I've figured checkpoints are a must if Ethereum or Bitcoin want to maintain the integrity of their transaction history across the Blockchain. As for Bitcoin, devs do not care about finality because the cryptocurrency has never experienced a 51% attack (as far as I know). But in the case of Ethereum, that's another story since transactions were rolled back after the DAO hack which occurred in 2016.

I've read somewhere that the ETH dev team is planning to "punish" malicious validators (stakers) within the ETH blockchain. Validators would simply lose all of their ETH if they try to disrupt the Blockchain. Something like this should be implemented on the Bitcoin blockchain, but modified to work with its PoW consensus algorithm. Better yet, Bitcoin could adopt a multi-algo PoW model in order to maintain its integrity for the foreseeable future. Digibyte already has this, and it's one of the most secure cryptocurrencies of today. This coupled with checkpoints, should make Bitcoin transactions completely irreversible no matter what. Only then, true transaction finality will be achieved across the Blockchain.

Nonetheless, developers of the BTC blockchain are more focused on scalability than anything else. Their resources have shifted into the development of the Lightning Network which is bound to increase Bitcoin's adoption within the mainstream world. But I believe they should also focus on security/reliability by adding a decentralized checkpoint system in order to make Bitcoin transactions truly final. If there no interest/demand for something like this, there's the risk of someone altering Bitcoin's transaction history in the future. With the Chinese controlling more than 51% of BTC's hashrate, anything could happen. I hope that Bitcoin remains a censorship-resistant and truly decentralized cryptocurrency for years to come. Just my opinion :)

I want to know lately to find out about "Transaction Finality" on the Bitcoin blockchain. I have also been curious about how much confirmation is needed to actually verify a transaction, and why it is necessary to have more than one confirmation only to actually make a transaction successful. This creature says, what you know is if an input has "enough" (which can have various meanings) the amount of confirmation and you can or can't spend it (it's yours or not). I am somewhat confused by this, and I want someone to help me clarify this issue. ???

You can write the code yourself or submit a general idea about it. Let the community discuss and see if anyone picked your idea. In the worst scenario, there might be a fork or a split.

I believe security is always on their mind. No developer is stupid enough to ignore it. I'll ignore the 51% part, but just remember, just because you have the power to do it, doesn't mean you can ignore the cost to do it.

It's not that devs "don't care", it's that checkpoints turn it into a game of pot luck, creating disparity.  If 'user A' received their transaction before the checkpoint, their transaction is safe, but if 'user B' received a transaction after the most recent checkpoint, they could still lose their funds, destroying any faith they had that the blockchain is impartial, neutral or fair - all things we generally claim it to be.  

Or in reverse, users sending payments might profit illicitly if it was rolled back to a checkpoint and they got their BTC returned after using it to purchase a product or service.  How pissed off would you be if you were the merchant providing that service?  

So, if Bitcoin's security ever fails, it fails for everyone equally.  No two-tier lottery where some users win while others lose.

Worse still, game-theory seems to indicate that, understanding the above concept, it could conceivably create additional incentive to attempt a hashrate attack in order to game a checkpoint system.

Good point. It all depends on community consensus than anything else. If the BTC community approves checkpoints and other security mechanisms, I don't a reason why developers wouldn't care more or less about it. Security and decentralization has always been Bitcoin's "motto". I'm sure that developers, miners, and community members will work together in order to make Bitcoin the strongest Blockchain in the world. It's already the most secure Blockchain in the world, but there's still room for improvement.

As you've said earlier, anyone can write code or submit a general idea about it. There are many Bitcoin Improvement Proposals out there which are subject to the approval of the Bitcoin community. I believe that something as important as transaction finality should gather the attention of everyone in the BTC space once 51% attacks become a threat to the Blockchain. Considering that Chinese miners still control more than 51% of BTC's hashrate, anything could happen in the future. But knowing that malicious attackers would quickly lose their incentive/reward from the Blockchain, it's very unlikely such situation will happen by then.




In that case, Bitcoin should remain as it is right now. Adding complex features or improvements would only make matters worse, in my own opinion. Besides, there are other ways to maintain the integrity of BTC transactions without the need for checkpoints. If 51% attacks become a real threat to the Blockchain, developers could easily switch to a new PoW algo that's ASIC-Resistant. Or they could simply adopt alternative mining protocols like Betterhash or Stratum V2 in order to make mining more decentralized. Considering that Bitcoin's transaction history has remained intact since inception (AFAIK), I doubt the immutability of the Blockchain would be much of a concern in the future. Still, we should be prepared for any adverse situations that may happen in crypto land. It's in developer's best interests to maintain the BTC blockchain as secure and resilient as possible, in order to fulfil Satoshi's vision of a censorship-resistant and decentralized economy for the whole world to enjoy. Just my thoughts ;D

I once excessively got interested in what number of affirmation is required so on totally check an exchange, and for what reason does it must have in more than 2 affirmation just to totally made an exchange fruitful. With this respect, I even have came up to resolution that the exchange is extremely more made sure about based from the number of affirmation it gets from the diggers.

More often than not, the exchanges I've made is as of now been prepared with exactly in any event 3 affirmation on the system. :) :)