Epoch

An epoch is a fundamental time division in proof-of-stake blockchain protocols that organizes validator duties, reward distribution, and chain finalization. Different networks define epochs differently, but the core concept is the same: a recurring cycle that structures network operations.

On Ethereum, one epoch = 32 slots, each slot lasting 12 seconds, for a total of 6.4 minutes per epoch. In each slot, one validator is randomly selected to propose a block, and committees of validators attest (vote) on its validity. After two consecutive justified epochs (called Casper FFG finality), transactions achieve economic finality — meaning reversing them would require destroying at least one-third of all staked ETH (worth billions of dollars). This two-epoch finality means Ethereum transactions reach irreversibility in approximately 12.8 minutes.

On Cardano, an epoch lasts 5 days and determines stake pool delegation rewards. On Solana, epochs last approximately 2-3 days and determine when stake activations and deactivations take effect. Bitcoin doesn't use epochs in the PoS sense, but the difficulty adjustment period (every 2,016 blocks, roughly 2 weeks) serves a similar organizational function.

For investors, epochs matter most when staking: rewards are calculated per epoch, and unstaking usually requires waiting until the end of the current epoch (or multiple epochs). Understanding epoch timing helps set expectations for when staking changes take effect.