What Is a Hard Fork?
A hard fork is a change to the rules of a blockchain that older software cannot accept. Computers that run the network's software are called nodes, and each node checks every new block against a set of rules. When a hard fork activates, nodes that have not upgraded treat the new blocks as invalid, while upgraded nodes accept them. Unlike a soft fork, which stays compatible with older software, a hard fork can leave the two groups unable to agree on which history is correct, so the chain may split into two separate networks.
Hard forks are usually planned. Developers publish new software, and node operators, miners or validators, exchanges, and wallet providers decide whether to upgrade. A change might add a feature, alter how transactions are processed, modify the consensus mechanism, or reverse past transactions in response to a serious problem.
How a Hard Fork Plays Out
Before the activation point, the network runs one set of rules. After it, two sets of rules may exist. If most participants upgrade and the rest do not, the minority may stop producing valid blocks, and the original chain may effectively continue under the new rules. If a significant group refuses to upgrade, both chains can keep operating, each with its own coins and transaction history.
When a split happens, holders of the original coin may find they also hold coins on the new chain, but whether they can access them depends on the case. Ownership details and tax treatment can be complicated, so outcomes vary.
An Example
In 2016, the Ethereum network carried out a hard fork to reverse the effects of a theft from The DAO, a fund run through a smart contract. Some community members rejected the change and kept the original chain running, which became Ethereum Classic. The two networks have operated separately since then. Bitcoin Cash, which appeared in 2017, is another case where a disagreement over block size led to a split from Bitcoin.
Why It Matters to Investors
Hard forks can create new cryptocurrency tokens, change how a network works, and introduce uncertainty about exchange listings and wallet support. Investors may need to follow announcements about which chain a platform supports. The impact on any specific asset depends on the details of the fork, so official project documentation is a common starting point. A hard fork is not guaranteed to succeed, and a split can reduce liquidity or confidence in either version.
Updated October 26, 2026. For general education only; not financial, tax or legal advice.