As of October 2026, roughly 20.1 million bitcoin have been issued, out of a maximum of 21 million that will ever exist. That is about 95.7 percent of the total supply, mined in seventeen years; the remaining 4.3 percent trickles out over the next century, with the last fraction expected around the year 2140.
Those numbers raise the three questions this guide answers: where does the 21 million figure come from, what enforces it, and how much of the issued supply is actually available.
Where does the 21 million cap come from?
The cap is not a promise or a policy; it is arithmetic baked into the issuance schedule. New bitcoin enters circulation only one way, as the reward miners collect for adding each block of transactions to the ledger. The schedule works like this:
- Blocks arrive roughly every ten minutes.
- The reward started at 50 bitcoin per block in January 2009.
- Every 210,000 blocks, about four years, the reward cuts in half: 50, then 25, then 12.5, then 6.25, then 3.125 since April 2024.
Sum that shrinking series over all future halvings and it converges just under 21 million. There is no vault holding unissued coins and no committee deciding the pace; the supply curve was published in the code on day one and has run on schedule ever since. The halving mechanism and its market folklore get their own guide in What Is the Bitcoin Halving, and the full dates-and-numbers table lives in Bitcoin Halving Dates.
What actually stops someone from issuing more?
A number in code sounds fragile; could it not be edited? Technically, anyone can edit their own copy of the software. What they cannot do is make the rest of the network accept it. Every one of the tens of thousands of independent nodes validates every block against the issuance rules, and a block that mints coins ahead of schedule is rejected automatically, regardless of who mined it or how much computing power they spent. Changing the cap would require essentially the entire economy of bitcoin users, holders, miners and businesses to voluntarily adopt new software that dilutes their own holdings. The security model behind this is covered in What Is Blockchain? and What Is Bitcoin Mining.
This enforcement-by-everyone is the substantive difference between bitcoin’s cap and any institutional promise of scarcity. It is also, bluntly, the entire pitch: a monetary asset whose supply schedule does not bend to circumstances. Whether that property matters is a judgment; that bitcoin has it is a verifiable fact, and the valuation debate it feeds is handled honestly in What Gives Bitcoin Value.
How much of the supply is really available?
The issued figure overstates what could ever come to market, because a meaningful slice of bitcoin is gone for good.
Lost coins. Keys thrown out with old hard drives, forgotten passphrases, holders who died without succession plans. Estimates are necessarily rough; studies of long-dormant coins commonly place permanent losses in the range of 3 to 4 million bitcoin, much of it from the early years when coins were nearly worthless and casually handled. Lost coins remain visible on the ledger forever but can never be spent, making the effective supply closer to 16 to 17 million.
Satoshi’s coins. Within that dormant pile sits the most watched subset: the roughly one million bitcoin attributed to the founder’s early mining, untouched since 2010, a story told in Who Created Bitcoin?.
Concentrated long-term holdings. Beyond what is lost, a large share of supply sits with holders who rarely move coins: individuals holding across cycles, corporate treasuries, and since 2024 the spot ETFs, which by 2026 had accumulated well over a million bitcoin on behalf of their shareholders. The ledger lets analysts measure this hoarding directly, cohort by cohort; the breakdown lives in Who Owns the Most Bitcoin? and the behavioral split in Long Term vs Short Term Holders.
The practical takeaway: daily trading happens on the thin, liquid edge of a mostly still supply.
Does the smallest unit matter? You will never buy a whole coin anyway
Each bitcoin divides into 100 million units called satoshis, so the network’s real unit count is about 2.1 quadrillion sats. Divisibility means the fixed cap does not make the asset unusable at small scale: at the October 15, 2026 price near $82,300, ten dollars buys roughly 12,000 sats. The unit has its own short guide, What Is a Satoshi?.
What happens when the last bitcoin is mined?
Around 2140 the block reward reaches zero, and miner income becomes transaction fees alone. Whether fees will fund adequate security a century out is a genuinely open question, debated in good faith inside the industry; the fee market’s mechanics today are covered in Bitcoin Fees Explained. What the 2140 date does not mean is scarcity arriving suddenly: more than 95 percent of all bitcoin already exists today, and the remaining issuance is a long, thin tail. In supply terms, bitcoin is already nearly fully diluted, something few assets, and no fiat currency, can claim.
On the radar
Three numbers to keep: 21 million cap, about 20.1 million issued as of October 2026, perhaps 16 to 17 million effectively reachable. The cap is enforced by verification, not trust; the issued supply is public to the satoshi; the available supply is smaller than it looks. The next instrument is the event that sets the pace, in What Is the Bitcoin Halving.