Bitcoin's Block Reward, Block Size and Block Time: Three Numbers, One System
How these three interconnected variables actually work together to control Bitcoin's issuance, capacity and settlement speed.
By Firoz Khan|5 August 2026|Updated 11 October 2026|3 min read
Three specific numbers govern most of what people actually care about with Bitcoin, how fast new coins are created, how much the network can process, and how quickly a transaction settles. They're interconnected by design, not three independent settings.
Block reward: the coin issuance mechanism
Miners who successfully add a new block receive a fixed number of newly created bitcoins as a reward, alongside the transaction fees from that block. This reward halves roughly every four years, a scheduled event known as the halving, which is the actual mechanism enforcing Bitcoin's disinflationary, capped supply over time.
The reward halves every 210,000 blocks, which is about four years. After the halving in April 2024, each block creates 3.125 new bitcoin. At one block every ten minutes, that is about 144 blocks a day, or roughly 52,560 a year, which is around 164,000 new bitcoin a year at the current reward. The yearly figure is an approximation.
The full halving schedule
The reward started at 50 bitcoin per block and has halved every 210,000 blocks since, according to the Bitcoin Wiki. The table shows each era.
Bitcoin block reward by era
| Metric | Reward per block | Halving date |
|---|---|---|
| From block 0 | 50 BTC | Start of the chain |
| Block 210,000 | 25 BTC | 28 November 2012 |
| Block 420,000 | 12.5 BTC | 9 July 2016 |
| Block 630,000 | 6.25 BTC | 11 May 2020 |
| Block 840,000 | 3.125 BTC | 20 April 2024 |
| Block 1,050,000 | 1.5625 BTC | Not yet reached |
Dates as listed by the Bitcoin Wiki, checked 11 October 2026. The next halving is roughly four years after the last one, but the exact date depends on how quickly blocks are found, so any specific date is an estimate.
Why the supply stops just short of 21 million
Each halving cuts new issuance in half, so the total approaches 21 million bitcoin without ever quite reaching it. The Bitcoin Wiki puts the limit at 20,999,999.9769 bitcoin, because amounts are stored as whole numbers of the smallest unit, so the final rounding leaves a sliver unissued. It also says that, if mining power had stayed constant, the last bitcoin would be mined around 2140. That date is an estimate, because nobody can forecast mining power for over a century.
Block size: the capacity constraint
Each block has a maximum data size, which limits how many transactions can fit into it. This deliberate cap is what keeps running a full validating node accessible on ordinary hardware, a direct trade-off between raw transaction throughput and the accessibility that keeps the network genuinely decentralised.
Satoshi Nakamoto introduced an explicit block size limit of 1 MB in 2010. It became the effective limit on block size from 2013. The Segregated Witness upgrade, SegWit, later increased the effective capacity to between 2 and 4 MB without a hard fork. The block size debate was one of the most contentious in Bitcoin's history, and it is the origin of Bitcoin Cash, which split off in 2017.
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Block weight: how SegWit changed the limit
Since SegWit, Bitcoin counts block capacity in weight units rather than raw bytes. The rule in BIP 141 is that a block's weight must not exceed 4,000,000, where weight is three times the size of the block without signature (witness) data plus its total size including it. The old limit was 1,000,000 bytes in total. Signature data is effectively discounted, which is why a block can hold more transactions than the old 1 MB limit allowed.
Block time: the pacing mechanism
Bitcoin targets roughly ten minutes between blocks, enforced by the difficulty adjustment mechanism, which automatically recalibrates how hard the mining puzzle is based on how much total computing power is currently pointed at the network, keeping the pace roughly consistent whether a handful of miners or the entire global mining industry is actively competing.
The adjustment happens every 2,016 blocks, roughly two weeks. If the previous 2,016 blocks took longer than two weeks, difficulty falls, and if they took less, it rises, in proportion to how far off the pace they were.
Why blocks are not exactly ten minutes apart
Ten minutes is an average target, not a timer. Blocks are found by trial and error, so some arrive within seconds and others take half an hour. The difficulty adjustment steers the average. Every 2,016 blocks the network compares how long they took with a target of 1,209,600 seconds (two weeks) and resets the difficulty. Bitcoin's developer documentation says a single adjustment can raise difficulty by at most 300% or lower it by at most 75%.
When miners can spend the reward
A miner's reward cannot be spent straight away. The developer documentation says coinbase outputs must be at least 100 blocks old first, which protects against spending a reward from a block that later turns out to sit on a discarded fork.
How the three actually interact
A fixed block time and fixed block size together set a hard ceiling on Bitcoin's total transaction throughput, which is precisely why demand spikes translate into fee competition rather than the network simply processing more transactions to absorb it, this capacity ceiling is also the direct reason layer-2 solutions and other scaling approaches exist at all.
Where fees fit in
The whitepaper anticipated the reward running out of road. It says that once a predetermined number of coins have entered circulation, the incentive can transition entirely to transaction fees and be completely inflation free. Each halving makes the fee share of a miner's income matter more. For a UK miner, HMRC's guidance says that unless the activity amounts to a trade, the sterling value of the coins at the time you receive them is taxable as miscellaneous income, with appropriate expenses reducing the amount chargeable, and that Capital Gains Tax may apply when you later dispose of them.
Where to read more
- Network congestion explained: what happens to fees when blocks fill up
- Layer-2 blockchains explained: how scaling layers relate to the base chain
- Proof of work vs proof of stake: the two ways a chain reaches agreement
- Crypto taxes in the UK: what HMRC expects you to record
A reminder
The FCA risk warning still applies to higher-risk crypto content. Always assess how much risk you are willing to take before buying.
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