Check when clocks change in a time zone

The job

Daylight saving rules differ by zone and change over the years. Whether '9 AM in New York' means UTC-4 or UTC-5 on a given date decides whether your call lands at a civilised hour. The checker reads the browser's IANA data — the same rules your operating system uses — and shows the change instants for the year you ask about.

Checking a zone

Pick a zone from the list or type an IANA name like America/New_York, enter a year, and read the result: whether DST applies, the exact spring-forward and fall-back instants (in UTC and local time), the offsets on either side, and what the zone is doing right now.

• Zones that never observe DST (most of Asia and Africa) say so plainly.
• Southern-hemisphere zones change in opposite months — the output shows the actual instants rather than assuming north.
• Historical years reflect the rules as they were then.

Worked example

America/New_York in 2025: clocks spring forward on March 9 and fall back on November 2 — so a meeting on March 10 is EDT (UTC-4), not EST. The same week in London (March 30 switch) means a rare week where New York and London are only 4 hours apart.

Where it stops

Covers 1970–2100 from the browser's built-in data; earlier years are approximations and future legislation is unknowable — zones like Turkey have changed rules on short notice. It answers 'when does the clock change', not 'what time is it in Tokyo' — use the timezone converter for the second question.