If someone asked you how many blocks (or minutes) they should wait to make sure their Bitcoin (BTC) transaction is irreversible, would you know what to say? The “rule of thumb” would be between three to six blocks (around 30 to 60 minutes), but experts say it should be even more.
Different people could give different answers, and a recent post by Luke Dash Jr. (@LukeDashjr) — a Bitcoin Core developer — on X suggests that a 12-block waiting (around 120 minutes) is the safer approach, considering Bitcoin mining‘s current state.
Indeed, probably should wait a good 12 blocks now
— Luke Dashjr (@LukeDashjr) September 19, 2023With that in mind, Finbold went deeper into understanding what is the safer confirmation time for a Bitcoin transaction.
% Attacker Global Hashrate vs # Confs for 99.9% Certainty. Source: Jameson Lopp
Notably, this aligns with the answer Luke Dash Jr. gave about the 12 confirmations needed considering that two Bitcoin mining pools already have over 20% of the global hashrate. These are Foundry USA and Antpool, with 29.67% and 22.75% of the total hashrate in the last month, respectively.
Bitcoin mining pools 1-month hashrate ranking. Source: mempool.space
Therefore, the recommended waiting time will vary depending on the state of the network but also on the risk tolerance of the receiving part. Some centralized exchanges have chosen to wait for three blocks depending on the deposit size, while others require four, five, or even six blocks — each block having an average interval of 10 minutes.
