Bitcoin Forum

Hello, can a BTC transaction be cancelled before it has been confirmed, or is it that once broadcast it is not possible to cancel at any time ?

If i'm not mistaking, you can create a new output, using the same inputs as you used for the transaction to be cancelled. Make sure you have a higher fee for the new transaction...

I've never tried this myself, but i picked it up somewhere on this forum... Might be mistaking tough.

No, cancelling a transaction is before an after confirmation not possible. In theorie it can be done but you must have control over 51% of the bitcoin network.
Before confirmation you can double spend the bitcoins but that's different than cancelling.

Eventough doublespending isn't the same as cancelling, it does have the same effect more or less... At least, if the output from the double spend coins goes to your own address...
Offcourse you'll create a new transaction, and you lose the fee, which wouldn't happen if you could "cancel" a transaction.

When transaction "hanging" in network some wallets have option to fill up transaction fee - so we can say in other words that cancel present transaction and send one more with different fee, but it is the same transaction just fee is different.

Cancelling transaction is not possible.

it can only be rejected by the network, if for example it remian in the limbo for a certain time frame because you did not pay any fee or something like this

@merelcoin you are right, you can create a new transaction with the same inputs and change some small stuff like fee for example and broadcast the new tx as a double spend.

@aleandromagno, can you explain more about this, which wallet has this feature? is it in console with typing in code or is it like in the interface something called double spend with extra fees?

Well the same question was raised many tumes and only thing is that it can be cancelled by bitcoin network which will only happen when a double spend is detected.But it is not easy to execute  a double spend as most of the the wallets now doesn't allows that.You need to have knowledge to script some parts of bitcoin wallet.

Thank you all, I was worried if someone pays me in Bitcoin and I send them the goods before the first confirmation, just by seeing the transaction on the blockchain, he might cancel it before the first confirmation.
Thanks

it's impossible, but if the transaction won't be confirmed within 24-48 hours, it's cancelled

Agreed, it is not possible to cancel the ongoing transaction manually, but auto cancellation takes place as suggested by above guy only in very rare in which confirmation gets much delayed.

When you deal with a person It is recommended to send/deliver the goods after the first confirmation, for example the poloniex exchange shows the deposit bitcoin only after first confirmation.

Highly doubt it, that's why BTC is so popular amongst the dark web

AFAIK they are refering to "replace by fee" (RBF), which is possible with bitcoin core if the first TX allows it and its not actually available via the GUI. Its more a "its possible" thing. I dont know of any wallet that actually implements RBF all the way to the GUI.

Once the transaction is broadcast to blockchain, there is no way to cancel the transaction.

To be honest i never did that, but i read somewhere (probably here on bitcointalk) that this is possible in Electrum wallet.

I will try to find that thread..

Edit: I cant find this thread, but someone asked in behalf of his friend who sent transaction (probably) from blockchain wallet without fee, and transaction of course was hanging.. Someone give him advice to export keys to Electrum wallet because (as he said) there is option to fill/change transaction fee..
I don't remember whether it worked or not.

I red long time ago, that it can be done. I mean, you have really small window to do it. For sure you must do it before first confirmation, not sure if not even faster.
You then create new output somehow, there was webpage for that in past. My memory is failing me a little bit.

Only if you quickly double spend it, but its almost impossible to do it only if you are technologically expert.You need to be careful next time where you send.

i accidentally cancelled the transaction, i had lost connection when i transfered some bitcoin to my friend, thus in my exprienced you could cancell it when the transaction is processing but when bitcoin has transfered and still confirmed i must say that it's imposible to cancelled it or dispute due to it's irreversible nature, why some people choose bitcoin for transaction than other payment method of course because these reasons

Last time I checked, theres no such thing as reversal.

The only thing you can do is hope to contact the address owner, and re-send it back?

as I know you can't undo every bitcoin transaction, the only one can cancel your transaction if not get confirmation for a long time.

Sounds like a double spend to me.

As far as I know Bitcoin transaction cant be reversed and that what's actually making it so popular.

But u should wait until a transaction gets 7-8 confirmations in order to ensure that everything is alright as there is a possibility to be cancelled with no fees if not confirmed in 2 days.

Good luck mate.

A transaction can be forgotten by the network if it didn't get included in a block for a longer time (i think it's random, usually between 1 and 7 days???).

However, i wouldn't wait for 7-8 confirmations... Chances of your transaction being included in an orphaned block are really slim:
https://blockchain.info/charts/n-orphaned-blocks?timespan=30days&showDataPoints=true&daysAverageString=1&show_header=true&scale=0&address=
https://blockchain.info/orphaned-blocks

Also, once it's included in a non-orphaned block, it's no longer possible to do a double spend.

So, i think for smaller transactions 1-2 confirmations should be sufficient.

Offcourse, when buying a house, you still might want (a lot) confirmations, in case of a 51% attack or something.

There is no fixed time. You essentially have to wait until every single node has forgotten the transaction or (to make it invalid) until a different TX that spends the same coins is confirmed. There are unconfirmed TX on some blockchain explorers that are 5 months old. If only a single node remembers it can rebroadcast the transaction to remember all other nodes. This will fail though if a different TX spending the same input(s) is already confirmed.

If I remember, you also have participated in this discussion .. :) But im not sure it was around month ago. When the number of transactions has increased and there was a lot of problems due to too low fees
Mainly it was about to withdraw hanging transaction from blockchain wallet (because of low fee) and move it to different wallet ..

I dont remember honestly, I gave a lot of advice during the last high demand period on the network. I hope it helped. What you describe sounds like a double spend to me. The reason I think someone (or me) suggested to export to electrum was that blockchain.info does not allow you to "reset" the blockchain data. It will always see your last TX and thus not allow you to double spend it. Electrum can be reset to a state where it does not know about TX A, so its possible to create a TX B that double spends A.

For sure not you have given this advice .. hmm From this perspective, in fact it looks like a double spend .. but maybe I forgot some detail from this situation.
Anyway, it would be answer to the question whether it is possible to scam someone before the first confirmation.

Yes I can tell you from personal experience that this is 100% possible, and many cheaters / double spenders are able to do this every time!

Wew, I think bitcoin transaction is irreversible ( can't be cancelled). Can you give me url to that thread, I was curious to read. thank you

It is difficult to get it to work but yes, it is definitely possible to get a transaction cancelled. If a transaction hasn't been confirmed by the network for a long time, it gets returned to the sender.

Almost happen to me but after 24 hours it confirmed it is very rare for a transaction to get cancelled,this is what all users should be aware of their is no charge back on bitcoin so look closely on the address you are sending your bitcoin..

Exactly only in very fee transactions it takes such a long time for confirmation. So even at those instances cancellation is really and highly impossible.

no a bitcoin transaction can not be canceled because when a transaction occured then it permanently and anonymusly stores in the network and hence it is not modifiable because it is permanent but we can disturb the network a little which causes the double spending but that's a diffrent thing.no body can cancel a bitcoin transaction after it is broadcast

The system was not designed for that for security.

Transaction processed by blockchain is can never be cancelled.Once the bitcoin  was transfered from one wallet to another it can never be cancelled nor refund even if that bitcoin wallet was hacked and the bitcoin is transfered by the hacker.Once the bitcoin is sent it will undergo blockchain and wait for confirmation and it can never be canceled.

see this transaction , anyone know this is transaction  can cancel
Warning! this transaction is a double spend
https://blockchain.info/tx/91287d3ef3bbeb76bc5eb4eaeb1e23ae300f88054b9db98d9ab1bc444c7744bf

It is sad but scammers do this type of thing.  It is simple to solve though if you just wait for a few conformations.   So you can make a decision based off who your dealing with.... but waiting for a confirmations if selling something is what I consider good practice.

But it's kinda getting away from OP.  No a transaction cannot be canceled in that sense.  Double spend is a way to make it appear there is a transaction but it's really going to two places, but again waiting on confirmations will show if it was sent successfully.

this is first transaction go to my transaction  no confirm up today is 5 days, i withdraw from site , so unlucky

I think you are right, its double spend but with good intention to cancel transaction.
Its very technical stuff tho, doubt it anyone can do this. I head in past some website made it easier by some automation process but not sure.