The rule behind the 21 million figure
Bitcoin’s software limits the total number of coins that can ever be created to just under 21 million. The number is not typed into the code as a single constant. It follows from a schedule: each new block creates a fixed amount of new bitcoin, and that amount is cut in half every 210,000 blocks.
The first blocks, starting in 2009, created 50 bitcoin each. After 210,000 blocks the amount fell to 25, then 12.5, and so on. Add up the series and the arithmetic is simple: 210,000 blocks times (50 + 25 + 12.5 + 6.25 + …) is 210,000 times 100, or 21 million. In practice the total lands slightly below that, because amounts are tracked in whole units of one hundred-millionth of a bitcoin and fractions are rounded down at each step. The widely quoted real limit is about 20,999,999.98 coins.
How new coins enter circulation
There is only one way new bitcoin is created: the block subsidy. Each block contains a special first transaction, sometimes called the coinbase transaction, in which the miner who found the block collects the subsidy. Nobody receives coins from a company or central authority; the protocol pays out according to the schedule, and every node checks that a block claims no more than it is allowed.
Transaction fees are different. They are paid by users and move existing coins to the miner, so they do not add to supply. A miner’s total take from a block is the subsidy plus the fees in it. How bitcoin mining works in detail is covered elsewhere; for supply purposes, what matters is that the subsidy is the only source of new coins.
Because blocks arrive about every ten minutes on average, 210,000 blocks take a little under four years. That is the origin of the “four-year” rhythm people associate with halvings, although the timing depends on block production and is not tied to the calendar.
The issuance schedule
The table shows the first five periods. Dates are approximate, since each period ends at a block height rather than a date.
| Period (approx.) | Subsidy per block | Total coins issued by end of period |
|---|---|---|
| 2009 to 2012 | 50 | 10,500,000 |
| 2012 to 2016 | 25 | 15,750,000 |
| 2016 to 2020 | 12.5 | 18,375,000 |
| 2020 to 2024 | 6.25 | 19,687,500 |
| 2024 to about 2028 | 3.125 | 20,343,750 |
Each figure is the previous total plus 210,000 times that period’s subsidy. The pattern is front-loaded: by the end of the fourth period, roughly 94 percent of all coins that will ever exist had already been issued. The remaining few percent trickle out over more than a century, with the subsidy eventually reaching zero around the year 2140. After that, miners would be paid only through fees.
Scarcity is a feature of the rules, not a price promise
The phrase fixed supply is often used as shorthand for “Bitcoin is scarce”. It is true that the schedule is predictable and publicly known, which is unusual for a currency. But scarcity alone does not set a price. Many things are limited in number and attract little interest. Prices come from the interaction of buyers and sellers, so the broader idea of supply and demand is the useful frame: a limited supply only matters if there is demand for it, and demand can rise or fall for reasons that have nothing to do with the cap.
It is also worth being clear about what “fixed” means. The cap is enforced because the software that nodes run rejects blocks that break the rules. Changing it would require nearly everyone to adopt new software, and there has been no serious move in that direction, but it is a social and technical agreement rather than a law of physics. Describing it as very difficult to change is accurate; describing it as impossible goes further than the evidence.
Issued is not the same as available
The number of coins issued is not the number of coins usable today. Some coins are held in wallets whose keys have been lost, some are in addresses that cannot be spent, and some have not moved in many years. The topic of lost coins is a debate of its own, because it affects how scarce the supply really is. Data sites also report supply figures in slightly different ways, which is why you will see circulating supply quoted next to the maximum.
Supply growth is slow and shrinking
Since the 2024 halving, new issuance has been 3.125 coins per block. At roughly 144 blocks per day that is on the order of 450 coins per day, or about 164,000 per year, which is well under one percent of the existing total. The yearly issuance rate keeps falling at each halving, and an article elsewhere compares it with the growth of national money supplies. The point to keep in mind here is only that new supply is small relative to what already exists.
That has a practical consequence for market capitalization. Market capitalization is price multiplied by the supply figure used, so for Bitcoin it moves almost entirely with price rather than with changes in the number of coins. For other assets with large scheduled releases, the picture can be very different.
What supply knowledge can and cannot do
Understanding the schedule helps you read headlines critically. It lets you check claims such as “half of all remaining coins are mined in this period” or “supply is about to shrink”, and it explains why block rewards and miner revenue are discussed so often. It does not tell you where the price is going. Cryptocurrency prices are volatile, past performance does not predict future results, and people can lose all of what they put in. Nothing here is financial, tax or legal advice.