Timezone Handling Guide: Store UTC, Display Local in Every Stack
Best practices for timezone-aware applications. Store timestamps in UTC, convert at display time, and avoid common timezone bugs in web apps.
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Tags: developer-tools, timestamps, timezones
Timezone Handling Guide: Store UTC, Display Local in Every Stack Bad timezone handling causes bugs that only surface at specific hours, in specific locations, or during daylight saving transitions — making them genuinely hard to reproduce and diagnose. The fix is a simple rule that eliminates most timezone bugs before they happen: store UTC, display local. This guide implements that rule across JavaScript, Python, SQL, and common backend patterns. Why Local Time Storage Fails Suppose you store in New York (Eastern time). Is that before or after the DST clock change? On November 3, 2024, clocks roll back from 2:00 AM to 1:00 AM. The time on that day is ambiguous — it happened twice. If you store that as UTC ( or ), there is no ambiguity. Each UTC instant is unique. A second problem: local…
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