Time handling is one of the most error-prone areas in software development. Following established patterns prevents subtle bugs that can be extremely difficult to diagnose.
Store UTC, Display Local
Store all timestamps as UTC in your database. Convert to the user's local timezone only when displaying. This makes comparisons, sorting, and duration calculations straightforward. Include the original timezone for audit purposes if needed.
Use Proper Time Types
Use your language's timezone-aware datetime types. JavaScript: use Date with timezone libraries. Python: use datetime with pytz/zoneinfo. Never use naive datetimes that lack timezone information. Timestamps without timezone context are ambiguous.
Let Users Choose Their Timezone
Don't assume timezone from IP location—users travel. Let users explicitly set their timezone in preferences. Default to browser timezone but allow override. For organizations, consider organization-level timezone settings.
Handle Time Input Carefully
When users input times, clarify the timezone context. Is "3:00 PM" in their local time, the event's location time, or something else? Use timezone-aware pickers. Confirm timezone interpretation for important events.