Who decides what time zone a country uses?

Individual countries decide their own time zones. There is no international authority that assigns them. Countries set their UTC offset through legislation or executive decree, and they can change it at any time — as Nepal, Samoa, and other nations have done in recent history.

Why do some countries use half-hour or quarter-hour offsets?

Countries like India (UTC+5:30), Iran (UTC+3:30), and Nepal (UTC+5:45) chose offsets that better center their solar noon within the clock day, or adopted offsets for political reasons. The mathematical ideal of 15-degree zones is rarely followed exactly.

Can a country change its time zone?

Yes. Samoa switched from UTC−11 to UTC+13 in 2011 to align its business day with Australia and New Zealand. North Korea adopted its own “Pyongyang Time” in 2015, then abandoned it in 2018. Time zones are national policy decisions.

How Time Zones Are Determined

June 16, 2026

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Frequently Asked Questions

Who decides what time zone a country uses?: Individual countries decide their own time zones. There is no international authority that assigns them. Countries set their UTC offset through legislation or executive decree, and they can change it at any time — as Nepal, Samoa, and other nations have done in recent history.
Why do some countries use half-hour or quarter-hour offsets?: Countries like India (UTC+5:30), Iran (UTC+3:30), and Nepal (UTC+5:45) chose offsets that better center their solar noon within the clock day, or adopted offsets for political reasons. The mathematical ideal of 15-degree zones is rarely followed exactly.
Can a country change its time zone?: Yes. Samoa switched from UTC−11 to UTC+13 in 2011 to align its business day with Australia and New Zealand. North Korea adopted its own “Pyongyang Time” in 2015, then abandoned it in 2018. Time zones are national policy decisions.