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The Department of Consumer Affairs notified the Legal Metrology (Indian Standard Time) Rules, 2026 on 27 August 2026 under Section 52 of the Legal Metrology Act, 2009.
The rules make Indian Standard Time the sole mandatory time reference for legal, administrative, commercial and official purposes across India.
CSIR-National Physical Laboratory, New Delhi will continue to maintain UTC(NPLI), the primary time scale from which official IST is derived.
Official time will also be disseminated through Regional Reference Standards Laboratories and ISRO's NavIC satellite navigation system.
The rules come into force 180 days after publication in the Official Gazette, placing mandatory compliance around March 2027.
Coordinated Universal Time is not kept by any single clock. It is a paper timescale computed from hundreds of atomic clocks worldwide, and each country maintains its own physical realisation of it. India's realisation is UTC(NPLI), maintained by the CSIR-National Physical Laboratory in New Delhi using caesium atomic clocks and a hydrogen maser. Indian Standard Time is simply UTC(NPLI) advanced by 5 hours 30 minutes, corresponding to the 82 degrees 30 minutes East meridian. Until now, that time was authoritative by convention rather than by law, and different systems, from bank servers to power grid controllers, could drift or synchronise to foreign time servers. The new rules make the national realisation legally binding and prescribe the technical means, NTP for general computer clocks and the higher-precision PTP for telecom and industrial systems, by which critical sectors must lock on to it.
Simple Analogy: It is the difference between everyone agreeing informally that the clock tower shows the right time and a law saying every clock in town must be set from the clock tower, with an inspector who can check.
India's National Metrology Institute, custodian of national measurement standards, and the keeper of UTC(NPLI) from which official Indian Standard Time is derived.
Administers the Legal Metrology Act, 2009 and notified these rules; the legal metrology system covers weights, measures and now time as a legally enforceable standard.
Operates NavIC, India's regional satellite navigation system, which provides positioning, navigation and timing services and will now also carry official time.
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The Indian realisation of Coordinated Universal Time, maintained by CSIR-National Physical Laboratory and the reference from which official IST is derived.
Navigation with Indian Constellation, ISRO's regional satellite navigation system providing positioning, navigation and timing services.
Network Time Protocol synchronises computer clocks over ordinary networks; Precision Time Protocol delivers far higher accuracy for telecom and industrial systems.