Published 1 January 2025 · 4 min read

How to Convert Time Zones — A Simple Guide for Global Teams

If you've ever missed a meeting because you got the time zone wrong, you're not alone. Time zone conversion is one of those things that seems simple until daylight saving time gets involved. Here's how to get it right every time.

Understanding UTC offsets

Every time zone is defined by its offset from Coordinated Universal Time (UTC). London (GMT) is UTC+0 in winter and UTC+1 during British Summer Time. New York is UTC-5 in winter (EST) and UTC-4 in summer (EDT).

To convert between two time zones, you calculate the difference between their UTC offsets. If London is at UTC+1 and New York is at UTC-4, the difference is 5 hours — so 3pm in London is 10am in New York during summer.

The daylight saving trap

The biggest mistake people make is assuming the offset between two cities is always the same. It's not. DST transitions happen on different dates in different countries:

• UK and Europe — clocks change on the last Sunday in March and October.
• US and Canada — clocks change on the second Sunday in March and the first Sunday in November.
• Australia — clocks change in April and October (reversed seasons).
• Some countries (e.g. Japan, India, China) — don't observe DST at all.

This means the time difference between London and New York is sometimes 5 hours and sometimes 4 hours, depending on the time of year. For a few weeks in spring and autumn when only one country has changed clocks, the difference shifts temporarily.

Common mistakes to avoid

• Using a fixed offset — always check the offset for the specific date, not just "in general."
• Forgetting the date might change — converting from late evening in one zone might mean it's already the next day (or previous day) in the target zone.
• Confusing city names — Portland, Oregon (UTC-8) and Portland, Maine (UTC-5) are very different time zones.
• Ignoring half-hour zones — India (UTC+5:30), Nepal (UTC+5:45), and parts of Australia use non-standard offsets.

Tips for global teams

When scheduling across time zones, always specify the time zone explicitly (e.g. "3pm GMT" not just "3pm"). Consider using UTC as a neutral reference point. And if you're scheduling recurring meetings, double-check around DST transition dates — the meeting time may shift for some participants.

Related articles