When is the last coin mined?

[Lorenzo]

So if the rewards for a miner is only the transaction fees (which we assume will be decreased further) then the price of bitcoin would have to be really high relative to today's in order for mining to be profitable? What sorts of price levels would we be talking about?

The default transaction fee can be adjusted as the value of BTC dips and rises. If the BTC price drops to $10, it could be made higher. If it skyrockets, it could be made lower. Furthermore, what we call the "default transaction fee" isn't really enforced on a protocol level. It's just the fee that is recommended by the reference client and you can choose to include a higher or lower fee with your transactions if that is what you prefer. Miners aren't tied to it either as they can choose to reject transactions with a fee less than x BTC where the value of x may or may not be the default transaction fee.

The price of a single bitcoin in terms of fiat shouldn't make a difference as to whether or not mining for transaction fees is profitable. If the BTC price is low, a miner might get 0.5 BTC (maybe worth $10) from fees. If the BTC price is high, the same miner might get 0.0005 BTC (still worth $10) instead.

Mining works in a way that if it's too unprofitable and too many people start leaving, then the difficulty will adjust so that mining becomes easier. If it's too profitable and too many people start entering, then the difficulty will adjust so that mining becomes harder.

Additionally the total number of transactions per second also matters. More transactions would make a average lower transaction fee possible since miners would still get the same block reward. The total number of transactions per second should be higher once Bitcoin is mainstream.

[kpitti]

Also, will the transaction fee remain at the standard 0.0001 BTC? (Was it even always like this back in the early days?) If so, that could become quite a sum to pay for a transaction. And is there a limit to how low the block reward can be? Because if there isn't wouldn't that mean that the cost of a transaction is greater than the reward per block?

Transaction fee is not fixed and can be changed anytime. I suppose that with increasing number of transactions the transaction fee can be lower. The definition can be changed as bitcoin definition has some flexibility on this.
Mining needs to be kept forever.

[JaredStein]

Got so much information just from reading this thread, thanks to you all.

[Twipple]

Also, will the transaction fee remain at the standard 0.0001 BTC? (Was it even always like this back in the early days?) If so, that could become quite a sum to pay for a transaction. And is there a limit to how low the block reward can be? Because if there isn't wouldn't that mean that the cost of a transaction is greater than the reward per block?

Transaction fee is not fixed and can be changed anytime. I suppose that with increasing number of transactions the transaction fee can be lower. The definition can be changed as bitcoin definition has some flexibility on this.
Mining needs to be kept forever.

But doesn't the transaction fees have to be kept at 0.0001 min for any amount sent ? As using a lower makes it low priority and harder to confirm sooner ?

[rexxarofmoknathal]

Ah okay, makes sense. So who/what determines the TX fee? I understand how the mining power and BTC price would affect it, but what ultimately sets it? Is it different for each wallet, or is it constant throughout the entire bitcoin network?

[redsn0w]

Ah okay, makes sense. So who/what determines the TX fee? I understand how the mining power and BTC price would affect it, but what ultimately sets it? Is it different for each wallet, or is it constant throughout the entire bitcoin network?

The minimum fee suggested is 1000 satoshi/Kb, you decide the fee. If you want you can also put 0.01 btc as fee, but it is no sense (at the moment) because I think we will reach 0.01 btc (as fee) when the block reward will be less than 0.50 BTC and the fee will be more important than the reward block itself.

[manselr]

Question in the title. When is the last bitcoin mined?

2140 if all things go as expected, IE we don't end up all dead in some stupid war, or something terribly unexpected happens like SHA256 being cracked (unlikely).