Block Height
The count of blocks since the genesis block (which is at height 0).
Block height is the number of blocks between any given block and the genesis block, which sits at height 0. Block 1 is one above genesis. Block 840,000 - where the fourth halving landed in April 2024 - is 840,000 above it.
Height is the canonical way to refer to a point in Bitcoin's history. Timestamps are imprecise (miners control their own clocks within a window). Dates depend on calendar conventions. But block heights are integer, monotonic, and identical for every node on the network.
Most of Bitcoin's protocol-level events are scheduled by height, not by date:
- Halvings happen at heights 210,000, 420,000, 630,000, and so on (every 210,000).
- Difficulty retargets happen at heights that are multiples of 2,016.
- Soft forks activate by height as well. Under BIP 9, a change such as SegWit locks in when 95% of the blocks in a 2,016-block retarget period signal for it and goes live one period later; Taproot's Speedy Trial deployment used a 90% threshold plus a fixed minimum activation height, 709,632. Older forks such as BIP 34 and BIP 66 switched on in two steps: once 750 of the previous 1,000 blocks carried the new version number, the new rules applied to new-version blocks; once 950 did, they applied to every block.
If you want a single number that locates "what's happening on Bitcoin right now," it's the current block height. See the Node page for the live current height.
Key takeaways
- Counts blocks from the original genesis block
- Used for referencing specific points in the blockchain
- Essential for protocol events tied to block intervals
Corrected
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Was: The entry said soft forks such as Taproot, SegWit and BIP 66 activate when a target height is reached or when signaling thresholds clear in a retarget window.
Now: BIP 66, like BIP 34 and BIP 65, activated by a rolling supermajority of the previous 1,000 blocks, not by a retarget-window tally or a set height. The retarget-period tally is BIP 9's mechanism, used for SegWit, and Taproot's fixed minimum activation height of 709,632 was an addition to it. Details
Sources (7)
- BIP-34 - Block v2, Height in Coinbase: the genesis block is height zero; 75% and 95% rules over the last 1,000 blocks (2012)
- Bitcoin Core - src/validation.cpp: GetBlockSubsidy halves every 210,000 blocks; ContextualCheckBlockHeader bounds a block's timestamp between median time past and two hours ahead (accessed 2026-10-13)
- Bitcoin Core - src/pow.cpp: the target changes only once per DifficultyAdjustmentInterval of 2016 blocks (accessed 2026-10-13)
- BIP-9 - Version bits with timeout and delay: signalling tallied per 2016-block retarget period, 95% threshold; BIP 34's supermajority rule reused by BIP 66 and BIP 65 (2015)
- BIP-341 - Taproot, Deployment: 90% threshold and min_activation_height 709632 (2020)
- Bitcoin Core - 0.21.1 release notes: taproot activation managed by a variation of BIP9 called Speedy Trial, 90% of a 2,016-block retarget period, active as of block 709632 (2021-05-01)
- mempool.space - Block 840000, the fourth halving (2024-04-20)
External references (1)
Related terms (14)
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