Bitcoin's Controlled Supply

Bitcoin's maximum supply is usually quoted as "21 million BTC," but the precise figure is 20,999,999.9769 BTC. The reason lies in how the halving is computed. Block rewards are tracked as integers in satoshis, and halving is not a division by two but a one-bit right shift of that integer. Whatever does not divide evenly is truncated at that moment and never issued.

Truncation first bites in Era 11, once the reward has become small, and the shortfall accumulated from there to the end totals about 0.0231 BTC, exactly the gap to a round 21,000,000. The final block reward does not leave a tiny remainder: it lands cleanly on 0 satoshis, by the mechanism described in the next section.

The smallest unit of Bitcoin is 1 satoshi (0.00000001 BTC). Expressed in satoshis, the maximum supply is 2,099,999,997,690,000, or roughly 2.1 quadrillion usable units.

The number "21,000,000" comes from 210,000 blocks × an initial reward of 50 BTC × the sum of the geometric series (Σ 1/2^n for n = 0 to infinity, which equals 2). That mathematical tidiness reflects Satoshi Nakamoto's design philosophy.

The block reward halves every 210,000 blocks (approximately 4 years). After a total of 33 halvings, the block reward reaches 0 satoshis.

Era 1 (Blocks 0–209,999): 50 BTC/block → Total: 10,500,000 BTC

Era 2 (Blocks 210,000–419,999): 25 BTC/block → Total: 5,250,000 BTC

Era 3 (Blocks 420,000–629,999): 12.5 BTC/block → Total: 2,625,000 BTC

Era 4 (Blocks 630,000–839,999): 6.25 BTC/block → Total: 1,312,500 BTC

Era 5 (Blocks 840,000–1,049,999): 3.125 BTC/block → Total: 656,250 BTC ← Current era

At block 6,930,000 (Era 34, around 2140), the reward drops to 0, and no new bitcoins will ever be created.

End of 2009: ~1.62 million BTC (first year's issuance; block height on December 31, 2009 was 32,489)

2012 (1st halving): ~10.5 million BTC (50% of total)

2016 (2nd halving): ~15.75 million BTC (75% of total)

2020 (3rd halving): ~18.375 million BTC (87.5% of total)

2024 (4th halving): ~19.6875 million BTC (93.75% of total)

March 2026: ~20 million BTC (~95.2% of total)

August 2026: ~20.07 million BTC (~95.6% of total) ← Current

2028 (5th halving, projected): ~20.34 million BTC (96.875% of total)

~2140: 20,999,999.9769 BTC (final value)

Assuming blocks are produced at exactly 10-minute intervals, the last bitcoin would be mined around the year 2140. The real average interval is slightly faster, about 9.62 minutes, and 17 years of that drift have accumulated, so the estimate carries no day-level precision. Read it as a rough year.

The theoretical maximum supply differs from the actual spendable supply. Many bitcoins have been permanently lost.

Genesis Block: The first 50 BTC cannot be spent because of a technical constraint in the protocol. Whether Satoshi did this on purpose, or it is a quirk of the code, is still debated.

Block 124,724: A miner claimed 1 satoshi less than the full reward. That satoshi is permanently lost.

Block 501,726: 12.5 BTC were destroyed by a faulty implementation.

Blocks 91,722/91,880 and 91,812/91,842: Duplicate transaction IDs rendered 100 BTC unspendable.

Beyond these technical losses, there are wallets with lost private keys and coins sent to unspendable addresses. Blockchain analytics firm Chainalysis published an estimate in November 2017 putting permanently lost bitcoin at 2.78–3.79 million BTC, or 17–23% of the supply issued at that time.

That figure is a statistical estimate built on the assumption that coins that have not moved for a long time are lost, and there is no technical way to distinguish long-term holding (hodling) from loss. It is also dated: it reflects neither coins lost since 2017 nor wallets that were written off and later recovered. The commonly quoted "3–4 million BTC" is not a settled number but a rounding of this single estimate.

After the last bitcoin is mined, miners' income will shift entirely from block rewards to transaction fees.

Section 6 ("Incentive") of the whitepaper states that once a predetermined number of coins are in circulation, the incentive can move entirely to transaction fees with no inflation at all. In Satoshi Nakamoto's exact words: "Once a predetermined number of coins have entered circulation, the incentive can transition entirely to transaction fees and be completely inflation free." That single sentence is the basis for the expectation that mining continues after the reward reaches zero.

Whether this transition proceeds smoothly is a central question for Bitcoin's long-term security. It turns on whether transaction volume and fees reach a sufficient level.

If Layer 2 solutions such as the Lightning Network become widespread, on-chain transaction counts may fall, which could affect fee revenue. The debate over this is known as the "security budget problem."

Bitcoin is divisible to 8 decimal places: 1 BTC = 100,000,000 satoshis. So even as coins are lost, the remaining supply can be subdivided to keep circulating.

In the future, protocol upgrades could allow even smaller units. The Lightning Network already uses millisatoshis (1/1000 of a satoshi).

When coins are lost, each remaining coin necessarily accounts for a larger share of the spendable supply. That much is simply arithmetic, with no exceptions.

"A larger share," however, is not the same as "a higher price." The latter holds only under the added assumption that demand stays constant; if demand falls, the price can decline even as supply tightens. The familiar line that loss amounts to appreciation for holders quietly skips that assumption. This site makes no price predictions.

People often compare this property to gold, but Bitcoin's supply schedule is far more precise and predictable than gold's.