Most people have a deeply ingrained misunderstanding about Bitcoin mining: they think the total supply is 21 million coins and that it will eventually be fully mined. But this understanding is actually flawed. From a mathematical perspective, Bitcoin is actually "never fully mined."

This goes back to Satoshi Nakamoto's initial design logic. Every 210,000 blocks, the block reward halves. In 2009, the reward was 50 BTC; after 12 years, it became 25 BTC; in 2016, 12.5 BTC; in 2020, 6.25 BTC; by 2024, only 3.125 BTC remains—this process will continue indefinitely.

The key point here is: it's not that the reward will suddenly drop to zero one day, but that it is a process that can never actually reach zero. In mathematical terms, this is a geometric series. The amount of new Bitcoin issued decreases more and more, but it can never hit zero in the final step. It's like pouring water into a cup, each time pouring only half, making the cup progressively emptier, but always leaving a little bit behind.

Bitcoin also has a minimum unit limit—called "Satoshi," which is 0.00000001 BTC. When the block reward shrinks to just 1 Satoshi, precise halving can no longer be executed. As a result, the reward approaches zero infinitely but never completely disappears.

Looking further ahead, around the year 2140, the new issuance of Bitcoin will essentially cease, but there will always be a tiny difference between the total supply and 21 million. That's why industry insiders often say it's "infinitely close to 21 million," rather than "exactly 21 million."

Since mining rewards are decreasing, why do miners still keep mining? The simple answer: transaction fees. As the block reward gradually diminishes, miners' income shifts from "new coin rewards" to "transaction fees." In fact, there are already examples where a single block's main revenue comes from fees, indicating that the economic incentives for mining won't disappear just because of halving.

Currently, nearly 20 million BTC have been mined, with less than 1.3 million remaining to be mined, and the issuance rate is slowing down. Thanks to this built-in, long-term predictable issuance mechanism encoded in the protocol, Bitcoin's scarcity increases over time. It's not a story of "being mined out" suddenly, but rather a gradual approach toward an ultimate limit over the long years.