TERM_DEF // UPGRADES_BIPS / BIP_113_MEDIAN_TIME_PAST_LOCKTIME
BIP 113 (MEDIAN
TIME PAST LOCKTIME)
TIME PAST LOCKTIME)
time-past-locktime/">BIP 113 (Median Time Past Locktime). Replacing block timestamp with MTP for locktime evaluation.
This page sits in the Upgrades & BIPs section — The proposal process and the major upgrades that shaped Bitcoin. Read on for what it is, why it exists, how it works under the hood, and what to watch out for.
This page sits in the Upgrades & BIPs section — The proposal process and the major upgrades that shaped Bitcoin. Read on for what it is, why it exists, how it works under the hood, and what to watch out for.
WHAT_BIP_113_MEDIAN_TIME_PAST_LOCKTIME_IS
BIP 113 (Median Time Past Locktime) — at a glance
UPGRADES
BIP 113 — "Median Time Past Locktime" is a proposal in the Consensus family, first published in 2016 with status final (fork/">soft fork). Replacing block timestamp with MTP for locktime evaluation. Its technical mechanism: replace nLockTime comparison with MEDIAN_TIME_PAST(11). protects against miner-time-tampering of locktimes
Why it exists
DESIGN
BIP 113 (Median Time Past Locktime) exists to solve a specific problem: use the past-11-block median time instead of the candidate block timestamp for locktime. Without a written, numbered spec, every wallet and node implementer would interpret the requirement differently — and Bitcoin's value depends on every implementation agreeing exactly. BIP-113 is the single source of truth for this concern, so any new client built today can match the behaviour of every client built since 2016.
HOW_IT_WORKS
Mechanism
HOW IT WORKS
Mechanically, BIP-113 replace nLockTime comparison with MEDIAN_TIME_PAST(11). Because this is a soft fork, old software accepts new behaviour without modification — but new behaviour is rejected if old software produces it. Adoption today: protects against miner-time-tampering of locktimes.
1. Author drafts BIP-113 against the BIP-2 template — abstract, motivation, specification, rationale.
2. The text + a reference implementation are posted on the bitcoin-dev list and as a PR to bitcoin/bips.
3. Reviewers tear it apart: ambiguities, security concerns, edge cases, interaction with prior BIPs.
4. Once stable, the BIP editor merges it; it gets a number (BIP-113) and the status "draft" or "proposed".
5. Implementations land in Bitcoin Core / wallets / other clients. For consensus changes: activation parameters chosen.
6. After deployment + adoption, BIP-113 is promoted to "final"; deprecated proposals get "replaced" or "withdrawn".
WORKED_EXAMPLE
BIP-113 — quick reference card
EXAMPLE
BIP number : 113
Title : Median Time Past Locktime
Area : Consensus
First published: 2016
Status : final
Fork class : soft
Motivation : use the past-11-block median time instead of the candidate block timestamp for locktime.
Mechanism : replace nLockTime comparison with MEDIAN_TIME_PAST(11).
Where it shows up : protects against miner-time-tampering of locktimes.
Read the spec : https://github.com/bitcoin/bips/blob/master/bip-0113.mediawiki
KEY_PROPERTIES
OPT-IN
No authority can force a BIP on anyone. Adoption depends entirely on whether the change is genuinely useful.
NUMBERED
Stable numeric reference — BIP-113 means the same thing across every wallet, miner, and node that has read this spec.
CONSENSUS
BIP-113 is a soft fork — it changes (or proposes to change) the rules every full node enforces.
DEPLOYED
Implementations of BIP-113 are in production. The behaviour is observable on mainnet today.
COMMON_PITFALLS
Things that catch people out
PITFALLS
- BIP-113 is a soft fork — old clients accept new behaviour but don't enforce it. Validate against an upgraded node to be sure the rule is being checked.
- Don't confuse "draft" / "proposed" / "final" status — read the BIP header before relying on it in production.
- The BIP number is just an editorial counter — it doesn't imply correctness or stability. Always cross-reference with the latest bitcoin/bips repo.
RELATED_CONCEPTS
Other terms from Upgrades & BIPs — click any to read its page:
TERMINOLOGY_INDEX
TERMINOLOGY
BIP 113 (Median Time Past Locktime)
Replacing block timestamp with MTP for locktime evaluation.
Segregated Witness (SegWit, BIP 141)
The 2017 upgrade separating witness-data/">witness data, fixing tx malleability, and introducing weight units.
Taproot (BIP 341)
Tapscript (BIP 342)
Script-language updates accompanying Taproot — new opcodes, removed limits.
Schnorr (BIP 340)
The Schnorr signature spec adopted by Taproot.
BIP Process
The community workflow for proposing, discussing, and tracking changes to Bitcoin.
Soft Fork Activation
MASF (Miner-Activated Soft Fork)
Activation triggered by miner signaling in block versions.