Convert meeting times between major time zones and compare offsets.
This tool provides estimates for informational purposes only and is not a substitute for professional advice. Individual results vary based on personal circumstances and assumptions.
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Time zones are one of those things that seem simple until you actually need to use them — then they quickly become confusing. Is New York 5 hours behind London or 6? Why does "EST" sometimes mean Eastern Standard Time and other times Eastern Time? What happens to meeting times during daylight saving transitions? This time zone calculator lets you convert any time from one zone to another instantly. This guide explains how the world's time zone system works, covers the most important US and UK time conversions, and explains how daylight saving time affects every clock on earth twice a year.
The world is divided into 24 primary time zones, each representing roughly 15 degrees of longitude (since 360 degrees ÷ 24 hours = 15 degrees per hour). All time zones are measured as an offset from Coordinated Universal Time (UTC), the international standard for timekeeping based at the Prime Meridian in Greenwich, London.
UTC+0 is Greenwich Mean Time (GMT) in winter — the baseline. Going east, zones add hours: UTC+1, UTC+2, up to UTC+12 and beyond. Going west, zones subtract hours: UTC-1, UTC-2, down to UTC-12. Some locations use half-hour offsets (India is UTC+5:30, Nepal is UTC+5:45) and some use 45-minute offsets.
In practice, political and geographic boundaries cause time zones to deviate significantly from the theoretical 15-degree lines. China, for example, uses a single time zone (UTC+8) across a country that spans what would naturally be 5 zones. The USA, by contrast, uses 6 time zones across the contiguous states plus Alaska and Hawaii.
The 48 contiguous US states span four main time zones. Alaska and Hawaii have their own. All US time zones shift by one hour during daylight saving time (DST), which begins on the second Sunday in March and ends on the first Sunday in November.
States included: New York, Florida, Georgia, North Carolina, South Carolina, Virginia, Pennsylvania, Ohio, Michigan, Indiana (most), and others along the East Coast and Midwest.
States included: Texas, Illinois, Minnesota, Wisconsin, Missouri, Tennessee, Louisiana, Alabama, Mississippi, Oklahoma, Kansas, and others in the central US.
States included: Colorado, Utah, Arizona (with exceptions), New Mexico, Wyoming, Montana, Idaho (most). Note: Arizona does not observe daylight saving time except for the Navajo Nation.
States included: California, Oregon, Washington, Nevada (most), and parts of Idaho.
The United Kingdom uses two time designations:
Note that GMT and UTC are often used interchangeably in everyday conversation, though they are technically different — UTC is an atomic time standard; GMT is a time zone. For practical purposes the difference is less than a second and irrelevant for scheduling.
The offset between the USA and UK changes depending on both countries' daylight saving transitions, which happen on different dates. There are typically four periods per year where the offset changes:
Quick reference for scheduling calls:
Key cities and their UTC offsets in standard time:
Daylight saving time shifts clocks forward by 1 hour in spring ("spring forward") and back 1 hour in autumn ("fall back"). The purpose is to shift an hour of daylight from the early morning to the evening — useful in high-latitude countries where summer days are very long.
USA DST dates:
UK/Europe DST dates:
Note that the US and UK transition dates differ, meaning there are typically 2–3 weeks each year where the US-UK offset is different from the usual value. This is a common source of scheduling confusion for transatlantic teams.
Countries that do not observe DST: Japan, China, India, most of Africa, and Hawaii (USA) and Arizona (USA, mostly) stay on the same time year-round.
In winter (both on standard time): 9 AM New York (EST) = 2:00 PM London (GMT). In summer (both on daylight saving): 9 AM New York (EDT) = 2:00 PM London (BST). The offset is 5 hours in winter and 4 hours in summer, but during transition weeks it can temporarily be 4 or 6 hours.
For everyday scheduling purposes, yes — they are functionally identical. Technically, UTC is a scientific atomic time standard while GMT is a geographic time zone. The difference is less than one second, which is irrelevant for any meeting or planning purpose.
The US and EU/UK adopted different dates for DST transitions. The US changed to "second Sunday in March" and "first Sunday in November" in 2007. The EU/UK uses "last Sunday in March" and "last Sunday in October." This creates a 1–3 week period twice a year where the US-UK offset differs from the usual.
Coordinated Universal Time — a compromise between the English abbreviation (CUT) and the French (TUC), resulting in UTC. It is the primary international time standard from which all time zones are calculated.
Disclaimer: Time zone information is based on standard international rules. Daylight saving changes can be altered by legislation — always verify current offsets for critical scheduling.