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What is a hard fork?
A hard fork is a change to a blockchain's rules that loosens or breaks them, so blocks made under the new rules are rejected by nodes that have not upgraded. If some participants never upgrade, the chain splits permanently into two, each with its own history from the split onward.
What it means for you
If a hard fork splits a chain, balances from before the split are recorded on both chains, because both share that earlier history. Whether coins on either side can be moved or sold depends on wallets, nodes and exchanges choosing to support that chain.
How it works
Under a hard fork, a block following the new consensus rules is accepted by upgraded nodes but rejected by non-upgraded ones. If miners divide between the two rule sets, non-upgraded nodes keep extending the old chain while upgraded nodes extend the new one, leaving permanently divergent chains. A soft fork avoids this by only tightening the rules, so old nodes still accept new blocks; with a hard fork, every node that wants to stay on the new chain has to upgrade.
Source: Bitcoin Developer Guide: Block Chain (consensus rule changes) · checked 4 October 2026
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