Should I store dates in UTC or local time in my database?

Always store timestamps in UTC. Local time is ambiguous during DST transitions and loses meaning when users move between zones. Convert to local time only at the presentation layer, using the IANA zone identifier to perform the conversion.

What is the IANA time zone database?

The IANA time zone database (also called tzdata or the Olson database) is the authoritative source of time zone rules used by virtually every operating system, programming language, and database engine. It maps identifiers like America/New_York to historical and current offset and DST rules.

How do I test my application across time zones?

Write unit tests that cover DST transitions, UTC date boundaries, and zones with unusual offsets like UTC+5:45. Use dependency injection or environment variables to override the system clock, and always test the spring-forward gap and fall-back overlap scenarios.

Time Zones in Software Development

July 23, 2026

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Frequently Asked Questions

Should I store dates in UTC or local time in my database?: Always store timestamps in UTC. Local time is ambiguous during DST transitions and loses meaning when users move between zones. Convert to local time only at the presentation layer, using the IANA zone identifier to perform the conversion.
What is the IANA time zone database?: The IANA time zone database (also called tzdata or the Olson database) is the authoritative source of time zone rules used by virtually every operating system, programming language, and database engine. It maps identifiers like America/New_York to historical and current offset and DST rules.
How do I test my application across time zones?: Write unit tests that cover DST transitions, UTC date boundaries, and zones with unusual offsets like UTC+5:45. Use dependency injection or environment variables to override the system clock, and always test the spring-forward gap and fall-back overlap scenarios.