The Supply Schedule

Where you're going: You'll understand exactly where the 21 million number comes from, why the actual cap is 20,999,999.9769 BTC (not a clean 21M), and why this schedule is enforced not by a promise but by every node on Earth.

1. The 21 Million Number

If Bitcoin had a slogan, "21 million, forever" would be it. The cap is mentioned in every introductory article, plastered on every conference t-shirt, and tattooed on a non-trivial number of forearms.

It's also the easiest claim to verify and one of the hardest claims to actually break. Most people who repeat it don't know where the number comes from. Let's fix that.

The cap is not a constitutional amendment. It is not a federal mandate. It is not a corporate policy. It is the sum of an infinite geometric series that every Bitcoin node calculates on every block, forever.

If a miner tried to issue more than the schedule allows, every other node would reject the block. The math is in the code, the code runs on tens of thousands of computers, and changing it would require near-universal coordination across people who genuinely don't want it changed.

It's the most boring kind of scarcity. It's also the most reliable kind ever invented.

2. Where It Comes From

The supply schedule is defined in GetBlockSubsidy, a function in Bitcoin Core's source code. The math:

• First block reward: 50 BTC
• Halving interval: every 210,000 blocks (about every 4 years at 10-minute average block time)
• Halving rule: the reward halves at each interval and rounds toward zero in satoshi precision

That's it. Three numbers and one rule. The cap is what falls out.

3. The Issuance Curve

Each "era" between halvings produces a fixed amount of new bitcoin:

Era 0:  50 BTC × 210,000 blocks   = 10,500,000 BTC
Era 1:  25 BTC × 210,000 blocks   =  5,250,000 BTC
Era 2:  12.5 BTC × 210,000 blocks =  2,625,000 BTC
Era 3:  6.25 BTC × 210,000 blocks =  1,312,500 BTC
Era 4:  3.125 BTC × 210,000 blocks =   656,250 BTC
Era 5:  1.5625 BTC × 210,000 blocks =  328,125 BTC
...

Adding these up gives you a geometric series:

S = 50 × 210,000 × (1 + 1/2 + 1/4 + 1/8 + 1/16 + ...)
S = 10,500,000 × 2
S = 21,000,000

The series converges to exactly 21 million in the mathematical limit. In practice, satoshi-level rounding (the reward drops below 1 satoshi after enough halvings) means the actual cap is 20,999,999.9769 BTC, give or take a sat.

The "missing" 0.0231 BTC isn't a bug. It's the floor on what can be expressed in 8 decimal places. After block ~6,930,000 (sometime around the year 2140), the subsidy rounds to zero satoshis and no more bitcoin will ever be issued.

4. The Halving Schedule

We covered this briefly in Chapter 2 of the Journey. Here it is in full detail:

Halving	Block	Date	New reward	Cumulative supply
Genesis	0	Jan 3, 2009	50 BTC	0
1st	210,000	Nov 28, 2012	25 BTC	10,500,000
2nd	420,000	Jul 9, 2016	12.5 BTC	15,750,000
3rd	630,000	May 11, 2020	6.25 BTC	18,375,000
4th	840,000	Apr 19, 2024	3.125 BTC	19,687,500
5th	1,050,000	~2028	1.5625 BTC	20,343,750
6th	1,260,000	~2032	0.78125 BTC	20,671,875
7th	1,470,000	~2036	0.390625 BTC	20,835,937.5
...	...	...	...	...
32nd	~6,720,000	~2136	~1 sat	~20,999,999.98
33rd	~6,930,000	~2140	0 sat (rounds down)	20,999,999.9769

Each halving cuts the new supply rate in half. The first four halvings issued 19,687,500 BTC, about 94% of the total. The remaining 28 halvings spread the last 6% across more than a century.

This is what people mean when they say Bitcoin is front-loaded and disinflationary. Most of the supply is already out. The schedule approaches its asymptote at zero.

5. The 20,999,999.9769 Asymptote

The slightly-less-than-21M number is worth pausing on, because it gets at something interesting about Bitcoin's design.

Bitcoin tracks balances in satoshis, not BTC. One satoshi is the smallest representable unit: 1 / 100,000,000 of a BTC. (See the Bitcoin Units rabbit hole for a full walk through the scale.)

When you halve a reward, you halve the satoshi count. 50 BTC = 5,000,000,000 satoshis. After 1 halving: 2,500,000,000. After 2: 1,250,000,000. And so on.

Eventually you reach a halving where the reward is below 1 satoshi. At that point, integer division by 2 produces 0. There's nothing smaller than a satoshi (on the base layer, anyway), so the subsidy becomes zero and stays there.

This happens at halving 33, somewhere around the year 2140. The total supply at that moment is 20,999,999.9769 BTC. That's the actual cap. The "21 million" is a marketing-friendly rounded version.

6. Inflation Rate Today vs. Gold

Bitcoin's annual inflation rate is the new supply being issued each year divided by the total existing supply. Let's compute the current value:

• Current subsidy (era 4): 3.125 BTC per block
• Blocks per year: ~52,560
• Annual issuance: 3.125 × 52,560 = 164,250 BTC per year
• Total supply (mid-era 4): ~19,867,581 BTC
• Annual inflation: 164,250 / 19,867,581 = ~0.83%

For comparison:

• Gold: historically ~1.5-2% annual supply growth from mining
• USD M2: averaged ~7% annual growth from 1971-2024 (much higher during 2020-2022)
• Most fiat currencies: 2-10% in stable economies, much higher in unstable ones

After the next halving (block 1,050,000, around 2028), Bitcoin's annual issuance will drop to ~82,125 BTC, and its inflation rate will halve to roughly 0.4%.

Bitcoin's monetary expansion rate is already lower than gold's. That's a remarkable fact and one most people get wrong.

Live supply

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Circulating is from gettxoutsetinfo on a live Bitcoin node, served via ChainQuery.com. The true asymptote is 20,999,999.9769 BTC (rounding leaves 0.0231 unminable); the bar is drawn against that, not a clean 21M.

7. The Social Contract Argument

The 21 million cap is enforced by code, not by promise. But code can be changed. So the deeper question is: why won't it be?

Three reasons, in order of importance:

1. Enforcement is distributed. Every full node validates every block against the supply schedule. To raise the cap, you'd need not just developer agreement, but for every node operator on Earth to run the new software. Node operators are, definitionally, people who care enough about Bitcoin to validate it themselves. They are the least likely demographic to accept a supply increase.

2. The cap is the value proposition. People hold Bitcoin precisely because the supply is fixed. Raising the cap destroys the only durable reason to hold it instead of any other asset. This is not a technical observation; it's an economic one. The first vote to raise the cap is the last day Bitcoin is worth anything.

3. There's no one to ask. Bitcoin has no CEO, no board, no foundation, no Satoshi. Even if someone wanted to raise the cap, there is no central party with the authority to propose it credibly. Any proposal becomes a fork, and the fork that keeps the 21M cap is, by every economic measure, "real Bitcoin." The fork that raises it becomes an altcoin overnight.

This isn't a guarantee. It's a Schelling point so strong that arguing against it has never been a serious project. In sixteen years of Bitcoin's history, no proposal to raise the cap has gotten meaningful traction. The closest thing was the 2017 "scaling debate," which was about block size, not supply, and which the 1MB-block side decisively won.

8. After Block ~6,930,000

When the last satoshi is mined around the year 2140, miners stop receiving any new bitcoin. From that point forward, their entire revenue comes from transaction fees - the small amounts users attach to transactions to incentivize inclusion.

This is sometimes posed as a worry: will miners still mine if there's no subsidy? The answer, as we've come to see, is yes, as long as transaction volume + fees + bitcoin's value combine to make the energy investment worthwhile.

In practice, fees have been growing as a percentage of miner revenue for years. By 2140, the network expects them to be the entire compensation. The economics work out as long as Bitcoin is being used at all.

This is also why scaling Bitcoin matters - the Lightning Network, batching, and second-layer protocols all reduce on-chain transaction volume per user but increase the value moving through Bitcoin, which translates to higher per-byte fees, which keeps miners paid.

The 21 million cap is the monetary policy. The fee market is the security policy. Both are in the code. Neither has a backdoor.

9. What This Buys Us

The 21M cap is the single most boring fact about Bitcoin, and the single most consequential.

It means:

• Your savings cannot be diluted. No one can print more Bitcoin to fund anything. Not a war, not a stimulus, not a bailout, not a vote-buying program.
• The supply schedule is the same in 2140 as it is today. You can plan around it across human lifetimes.
• There is no "growth target." The Federal Reserve targets 2% inflation. Bitcoin targets none. Bitcoin doesn't target anything. It just runs.

That's the deal. Boring, fixed, verifiable, durable. A monetary system without a steering wheel.

Pro tip: When someone tells you "Bitcoin's 21M cap could change," ask them which specific change they think would pass. The honest answer is "none, ever," because there is no path to changing it that doesn't break Bitcoin as a thing worth changing. The cap is what holds.