DST Transition Lookup
Find the next DST start/end for any IANA time zone.
Overview
The DST Transition Lookup tool finds the next daylight-saving start and end for any IANA time zone. Pick a zone like Europe/London or America/New_York and the tool returns the upcoming "spring forward" and "fall back" instants, along with the UTC offset on each side of each transition.
Useful for SRE teams scheduling maintenance windows that need to avoid the ambiguous hour, calendar app developers testing edge cases, support engineers debugging a "the meeting moved by an hour" report, and travellers checking whether DST is active when they arrive.
How it works
The lookup queries the IANA time zone database (tzdata, also known as the Olson database), which is the authoritative source for civil time rules worldwide and ships embedded in .NET via TimeZoneInfo. The tool walks the future adjustment rules for the chosen zone and returns the next transition forward in time from the current instant, then the one after that.
Some zones (most of Asia, Africa, and US Arizona) never observe DST at all and return no upcoming transitions. Other zones change their rules over time as countries adopt or abandon DST — the tzdata snapshot bundled at build time is the source of truth, so very long-range queries may shift if a country changes its policy after release.
Examples
Europe/London
→ Next spring forward: 2026-03-29 01:00 UTC, offset +00:00 → +01:00
→ Next fall back: 2026-10-25 01:00 UTC, offset +01:00 → +00:00
America/New_York
→ Next spring forward: 2027-03-14 02:00 local, EST → EDT
→ Next fall back: 2026-11-01 02:00 local, EDT → EST
Asia/Tokyo
→ No DST transitions (zone is fixed at +09:00)
FAQ
Why do different zones spring forward on different dates?
Each country sets its own rules. The EU shifts on the last Sunday of March, the US on the second Sunday of March, Australia on the first Sunday of October, and so on.
Will my country still have DST next year?
The tool reflects current tzdata at the time of release. If your government enacts a law to abolish DST after that, the result becomes stale until the database is updated.
What is the ambiguous hour?
When clocks fall back, the same local time happens twice — for example 01:30 occurs once at offset +01:00 and again at +00:00. Logging events with their UTC offset removes the ambiguity.
What is the missing hour?
When clocks spring forward, the local time between 02:00 and 03:00 (or 01:00 and 02:00) does not exist. Calendar systems usually round skipped events forward to the next valid instant.
Does it handle Northern and Southern Hemisphere zones correctly?
Yes — the IANA database encodes the seasonal direction, so Southern Hemisphere zones like Australia/Sydney correctly spring forward in October and fall back in April.