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Halvings

7 min read

The reward for finding a block is cut in half every 210,000 blocks, roughly every four years, until issuance eventually stops near 21 million bitcoin.

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The block subsidy, newly issued bitcoin paid to a miner via the coinbase transaction, halves every 210,000 blocks. At roughly 10 minutes per block, that is close to four years, though the actual interval varies with real block production speed. The subsidy began at 50 BTC in 2009, dropped to 25 BTC in 2012, 12.5 BTC in 2016, 6.25 BTC in 2020, and 3.125 BTC in 2024.

This halving schedule, not a fixed annual percentage, is what defines Bitcoin's issuance curve. Because each halving is applied to an already-halved amount, the subsidy approaches, but never in practice reaches by continuous decay, zero: it is implemented with integer satoshi arithmetic, so after roughly 33 halvings (around the year 2140) the subsidy rounds down to 0 and no further new bitcoin is issued by this mechanism.

The oft-cited 21 million figure is the sum of this entire geometric-like sequence of subsidies, not a number stored anywhere as a target, it emerges from the schedule and the 10-minute block interval enforced by difficulty adjustment. It is an asymptote of the issuance formula rather than a hard-coded stopping cap checked at each block.

Explain more simply

When a miner finds a block, part of the reward is brand-new bitcoin created from nothing. That new-coin reward started at 50 bitcoin per block and gets cut in half on a fixed schedule.

This has happened four times so far, 50 to 25 to 12.5 to 6.25 to 3.125 bitcoin per block, and will keep happening roughly every four years until the reward eventually rounds down to zero.

Real-world analogy

Think of pouring water into a glass where each pour is half the size of the last: the glass gets fuller and fuller, but the amount added each time shrinks toward nothing without ever needing to hit exactly zero on paper.

Key facts

  • The block subsidy halves every 210,000 blocks, roughly every four years.
  • Subsidy history so far: 50 → 25 → 12.5 → 6.25 → 3.125 BTC per block.
  • 21 million is the emergent sum of the issuance schedule, not a value checked against directly by the code.

Common misconception

“Halvings automatically make the price of bitcoin double.”

A halving reduces the rate of new supply entering the market; it has no mechanical effect on demand or price. Historical price moves around past halvings do not guarantee future ones, and this course does not make price predictions.[1]

Go deeper

Because block times fluctuate around the 10-minute target rather than hitting it exactly, actual halving dates drift slightly against a naive four-year calendar expectation, for example, the 2024 halving occurred slightly ahead of a strict four-year mark from 2020, reflecting periods where average block times ran a little faster than target.

As the subsidy shrinks toward zero, the whitepaper's original argument is that transaction fees will need to supply an increasing share of miner revenue to keep sustaining the hash rate that secures the network; whether fee revenue alone will be sufficient long after 2140 is a subject of ongoing analysis rather than a settled certainty.

Quick check

Answer every question correctly (100%) to complete this lesson.

  1. 1.How often does the block subsidy halve?

    How often does the block subsidy halve?

  2. 2.Where does the 21 million bitcoin figure come from?

    Where does the 21 million bitcoin figure come from?

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Extra exam questions

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16 questions

Quick check

Answer every question correctly (100%) to complete this lesson.

  1. 1.What happens at a Bitcoin halving?

    What happens at a Bitcoin halving?

  2. 2.How often does a halving occur?

    How often does a halving occur?

  3. 3.What was the original block subsidy when Bitcoin launched?

    What was the original block subsidy when Bitcoin launched?

  4. 4.After the first halving, what was the block subsidy?

    After the first halving, what was the block subsidy?

  5. 5.What is the subsidy after the fourth halving (2024)?

    What is the subsidy after the fourth halving (2024)?

  6. 6.Why does the halving schedule exist?

    Why does the halving schedule exist?

  7. 7.What enforces the halving schedule?

    What enforces the halving schedule?

  8. 8.What determines exactly when a halving triggers?

    What determines exactly when a halving triggers?

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Sources