Time & Dates

What Is a Time Zone?

A time zone is a region that observes the same standard time. Time zones are defined by their offset from Coordinated Universal Time (UTC), such as UTC−5 or UTC+9. Their boundaries usually follow political borders rather than exact lines of longitude, and some regions use half-hour or 45-minute offsets.

IANA Names

Computer systems identify time zones with names such as America/New_York or Asia/Kolkata, which also store historical and daylight saving time rules.

Why Offsets Change

A zone's offset can change during the year because of daylight saving time, and governments occasionally change a region's standard offset or DST rules. Converting a time correctly therefore requires both the location and the specific date.

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Last updated: September 27, 2026. This definition is for general educational purposes only. It is not financial, investment, tax, legal, or medical advice, and it does not recommend any product or course of action. For decisions about your own situation, consult a qualified professional.