nLockTime

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nLockTime is a parameter of a transaction, that, if any input indicates so (by having nSequence not equal to UINT_MAX), mandates a minimal time (specified in either unix time or block height), before which the transaction cannot be accepted into a block. If all inputs in a transaction have nSequence equal to UINT_MAX, then nLockTime is ignored.

Since BIP68, the lock time can either be absolute or relative. Given a transaction,

  • If the most significant bit (1<<31) of the nLockTime field is set (if the lock time is absolute)
    • If nLockTime < 500000000
      • Specifies the block number at which this transaction can be spent
    • Otherwise
      • Specifies the UNIX timestamp at which this transaction can be spent
  • Otherwise (if the lock time is relative)
    • If the 23rd bit (1<<22) is not set
      • The last 16 bits of the nLockTime field specify a relative time in units of 512 seconds. The transaction can only be included in a block if spending_tx_block_time > spent_tx_block_time + nLockTime * 512.
    • Otherwise
      • The last 16 bits of the nLockTime field specify a relative block height before which the transaction can not be included in a block. In other words it can be included if spending_tx_block_height > spent_tx_block_height + nLockTime

See Also