Bitcoin's 21 million cap and the halving, explained

How new bitcoin is created

Bitcoin has no central bank or company that issues coins. New bitcoin appear through mining: computers compete to add the next block of transactions to the blockchain, and the winner is paid. That payment, the block reward, has two parts. The block subsidy is newly created bitcoin. Transaction fees are what users attach to their payments to have them included, as our guide to why blockchain fees change explains.

The Bitcoin whitepaper puts it simply: the first transaction in each block "starts a new coin owned by the creator of the block", which "provides a way to initially distribute coins into circulation, since there is no central authority to issue them."

The mempool is the pool of unconfirmed transactions that each node keeps. The last step is what makes the schedule binding. Bitcoin Core, the reference node software, rejects any block whose first transaction "pays too much": more than the subsidy allowed at that height plus the block's fees. A miner who tried to award itself extra coins would only throw away its work.

Where the 21 million comes from

The subsidy was 50 BTC per block when Bitcoin launched in January 2009, and it halves every 210,000 blocks. With a target of one block every 10 minutes, that works out to roughly four years. In Bitcoin Core, the whole rule takes a few lines of code.

Add up every era (210,000 blocks at 50 BTC, then 210,000 at 25, and so on) and the total approaches 21 million without reaching it. Because amounts are rounded down to whole satoshis, the smallest unit at one hundred-millionth of a bitcoin, the true maximum is 20,999,999.9769 BTC. The subsidy reaches zero at block 6,930,000, which is expected around 2140.

Most of the supply already exists. Counting by the schedule, the 20-millionth bitcoin was created in block 939,999 on 9 March 2026, and about 20.09 million had been issued by block 969,080 on 29 September 2026, more than 95% of the cap. At 3.125 BTC per block and about 144 blocks a day, the network now adds roughly 450 bitcoin a day, or about 0.8% of the supply per year.

Every halving so far, and the next

Halvings are triggered by block height, not by the calendar, so a date is only certain once the block is mined. These dates come straight from the blockchain:

The fifth halving will happen at block 1,050,000. On 29 September 2026, 80,920 blocks were left. At the pace since the last halving, just under 10 minutes per block, that points to around mid-April 2028.

What a halving means for miners

For miners, a halving is an overnight pay cut. The subsidy per block halves, while electricity, hardware and hosting cost the same as the day before. Machines that were barely profitable can start losing money and get switched off.

Bitcoin absorbs the shock through its difficulty adjustment. Every 2,016 blocks, about two weeks, the network resets how hard it is to find a block so that blocks keep arriving about every 10 minutes. After the April 2024 halving, the adjustment on 9 May 2024 cut difficulty by 5.6%, a sign that some computing power had gone offline. Blocks kept coming, with fewer machines sharing the work.

Fees, the other part of the reward, swing widely. Block 840,000, the halving block itself, paid about 37.6 BTC in fees, more than 12 times its subsidy, on a day of intense demand for block space. In late September 2026, by contrast, fees made up less than 1% of what miners earned per block.

That contrast feeds a long-running debate about Bitcoin's "security budget", the total paid to miners for securing the network. The whitepaper expected that once enough coins were in circulation, "the incentive can transition entirely to transaction fees and be completely inflation free." Whether fees will pay for the same level of security as the subsidy shrinks is still an open question among developers and researchers.

Why the scarcity argument is debated

A fixed supply is often called "digital scarcity", and commentators frequently link halvings to bitcoin's price. The reasoning is that if demand holds steady while new supply shrinks, something has to give. Critics say the argument leaves too much out.

The objections run like this. Every halving is scheduled years ahead, so it surprises no one. Scarcity only matters if people want the thing, and plenty of rare things are worth little. And there have been just four halvings, each tangled up with other events: a pandemic in 2020, and the arrival of US spot ETFs about three months before the halving in April 2024. That is too little history to separate cause from coincidence.

Lost coins add uncertainty. Coins whose keys are gone stay on the ledger but can never move, so the usable supply is smaller than the issued supply, by an amount no one knows. Financial products blur the picture further: spot ETFs hold real bitcoin, while futures and other derivatives offer price exposure without holding any coins. None of this settles anything about future prices, and this guide makes no predictions.

What spot bitcoin ETFs changed

An exchange-traded fund, or ETF, is a fund whose shares trade on a stock exchange like a company's shares. A spot bitcoin ETF holds bitcoin itself rather than futures contracts. The US funds are technically trusts, which regulators call exchange-traded products, but most people call them ETFs.

For years, the US Securities and Exchange Commission (SEC) rejected proposals for such funds. That changed after August 2023, when a federal appeals court ruled that the SEC had failed to adequately explain why it approved two funds based on bitcoin futures but not Grayscale's proposed spot fund. On 10 January 2024, the SEC approved rule changes letting NYSE Arca, Nasdaq and Cboe BZX list eleven spot bitcoin products, and trading began the next day. The SEC's chair at the time, Gary Gensler, stressed that the agency "did not approve or endorse bitcoin."

What changed was access, not supply. Investors could now get bitcoin exposure in an ordinary brokerage account, while the fund stores the coins with a custodian. And because the funds hold real bitcoin, investor demand turns into buying or selling of actual coins. BlackRock's iShares Bitcoin Trust ETF alone reported holding 734,261 bitcoin on 30 June 2026, about 3.7% of all bitcoin issued by then. Flows run both ways: in the first half of 2026, that fund added 157,501 bitcoin and gave up 192,970 to meet redemptions.

The rules have kept evolving. At first, shares could be created and redeemed only for cash. In July 2025, the SEC let authorized participants, the large brokers that create and redeem shares, swap bitcoin directly for shares. In September 2025, it approved generic listing standards, so exchanges can list qualifying funds that hold spot commodities, crypto included, without a separate rule change each time.