Many people have a deeply ingrained perception of Bitcoin: a total supply of 21 million coins, which will be fully mined by the year 2140, after which miners will rely solely on transaction fees. But if you really do the math, you'll find an interesting phenomenon—Bitcoin actually can never reach this upper limit.

This is backed by a clever mathematical logic designed by Satoshi Nakamoto.

Bitcoin’s halving mechanism is straightforward: in 2009, miners received 50 coins for each block mined, and roughly every four years, this reward halves. It became 25 coins in 2012, 12.5 coins in 2016, 6.25 coins in 2020, and will be reduced to 3.125 coins in 2024. It seems simple, but in reality, this process never really reaches the end.

Imagine pouring a glass of water. The first time, you pour out half, leaving half a glass; then pour out half of the remaining water, leaving a quarter of a glass; continue pouring, and it becomes an eighth of a glass... You could keep doing this forever; in theory, you would never finish pouring. The Bitcoin mining process is exactly like that.

The true limit comes from a technical detail: the smallest unit of Bitcoin is 1 Satoshi, which is 0.00000001 BTC. When the block reward, through countless halvings, approaches 1 Satoshi, the system hits a snag—you can't give miners half a Satoshi as a reward. This means the block reward will eventually stabilize at some very tiny number, never fully disappearing. So from a mathematical perspective, the 21 million figure is actually just an upper bound that can never be truly reached.