A Practical Guide to Time Zones for Remote Work and International Travel

How time zones work

Time zones divide the world into regions that share the same local time. The reference point is Coordinated Universal Time (UTC), which is the successor to Greenwich Mean Time (GMT) and does not change with daylight saving time. Every other time zone is expressed as an offset from UTC — either ahead (positive) or behind (negative).

For example, US Eastern Time is UTC−5 in winter (Eastern Standard Time) and UTC−4 in summer (Eastern Daylight Time). London is UTC+0 in winter and UTC+1 in summer. Tokyo is UTC+9 year-round because Japan does not observe daylight saving time.

There are roughly 38 distinct UTC offsets in use worldwide, including several with 30- or 45-minute offsets (India is UTC+5:30, Nepal is UTC+5:45, parts of Australia are UTC+9:30). This is why time zone math sometimes produces surprising results.

Daylight saving time: the main source of confusion

Daylight saving time (DST) shifts clocks forward by one hour in spring and back in fall. The confusion arises because different countries switch on different dates — and many countries do not observe DST at all.

The United States switches DST on the second Sunday in March and the first Sunday in November. Most of Europe switches the last Sunday in March and the last Sunday in October. This means there are approximately two to three weeks each spring and fall when the offset between US and European time zones is one hour different from the usual gap. A call that normally runs at 3:00 PM London time might be 10:00 AM Eastern — or 9:00 AM Eastern — depending on whether Europe has switched yet.

Arizona (except the Navajo Nation) and Hawaii do not observe DST. Neither do most of the world's countries, including China, India, Japan, most of Africa, and most of the Middle East. When calculating time differences for any location, it is worth confirming whether DST is currently in effect there.

Common US time zones at a glance

• Eastern (ET): UTC−5 (EST) / UTC−4 (EDT) — New York, Miami, Atlanta, Boston
• Central (CT): UTC−6 (CST) / UTC−5 (CDT) — Chicago, Dallas, Houston, Minneapolis
• Mountain (MT): UTC−7 (MST) / UTC−6 (MDT) — Denver, Phoenix, Salt Lake City
• Pacific (PT): UTC−8 (PST) / UTC−7 (PDT) — Los Angeles, Seattle, San Francisco
• Alaska (AKT): UTC−9 / UTC−8 — Anchorage
• Hawaii (HST): UTC−10 — Honolulu (no DST)

Scheduling across time zones

The most reliable way to share a meeting time across locations is to use UTC as the common reference. "Let's meet at 15:00 UTC" is unambiguous — each person converts to their local time. This approach avoids misunderstandings caused by not knowing whether the sender is observing DST.

For recurring meetings with teams in multiple locations, it helps to pick a time that falls within standard business hours (roughly 9 AM to 6 PM) for as many participants as possible. A 9:00 AM Pacific meeting is noon Eastern and 6:00 PM London — workable. The same meeting for Tokyo would be 2:00 AM, which is not. Finding a window that works across more than two or three widely separated time zones often requires someone to accept an early morning or late evening call.

Tips for avoiding scheduling mistakes

• Always specify the time zone when scheduling, even within the same country — US time zones span three hours coast to coast.
• Use the city name rather than the abbreviation when possible. "EST" and "EDT" are both called "Eastern" but differ by an hour, and "CST" can mean Central Standard or China Standard depending on context.
• Confirm whether the other party's location currently observes daylight saving time, especially in the weeks around switching dates.
• When scheduling internationally, use a converter rather than mental math — even small errors (forgetting a half-hour offset, miscounting hours) can cause missed meetings.

Convert times and plan meetings

The free Time Zone Converter converts a specific time from one location to another. For finding meeting windows that work across multiple locations simultaneously, the Meeting Planner shows overlapping business hours across several time zones at once so you can pick the least painful slot for everyone involved.