Locktime
technical · blockchain
A transaction field or script condition that delays when a transaction or spending path becomes eligible for inclusion.
Locktime is a Bitcoin-style transaction feature that keeps a transaction non-final until a specified block height or time condition is satisfied. Related script opcodes can delay a particular spending path. These mechanisms support delayed settlement, refunds, and recovery paths.
The nLockTime field is a 32-bit value. Values below 500,000,000 are interpreted as block heights; values at or above that threshold are time-based and evaluated against the chain's applicable median-time-past rule rather than a user's wall clock. If every input sequence is final (0xffffffff), transaction-level nLockTime is disabled.
Timelocks are important for payment channels, atomic swaps, escrow, and recovery transactions. They give honest participants a window to claim, refund, or dispute funds without trusting a counterparty.
Related mechanisms include CLTV for absolute timelocks inside scripts and CSV for relative timelocks based on how long an output has existed. These tools are more flexible than a transaction-level nLockTime alone.
Related terms
Hash Time-Locked Contract (HTLC)
→A conditional payment that can be claimed with a secret before a deadline or refunded after the deadline.
smart-contract · payments · cryptography
Escrow
→Escrow holds funds until agreed conditions are met, using a trusted custodian, multisig, or smart contract logic.
finance · security
Confirmations
→The count of blocks confirming a transaction, usually including the block that first contains it.
security · blockchain