Time Zone Difference Calculator

Time Zone Guide

How Time Zones Work

The world is divided into 24 standard time zones, each covering 15° of longitude (one hour apart). UTC (Coordinated Universal Time) is the global reference point — previously called GMT (Greenwich Mean Time), which still defines UTC+0. Time zones are expressed as offsets from UTC: New York is UTC-5 (EST) or UTC-4 (EDT during daylight saving), London is UTC+0 or UTC+1 (BST), Tokyo is UTC+9 year-round, Sydney is UTC+10 or UTC+11 (AEDT).

Daylight Saving Time

Around 70 countries observe daylight saving time (DST), shifting clocks forward one hour in spring and back in autumn. This creates a complication: a fixed UTC offset does not tell you the current local time without knowing whether DST is in effect. The EU has voted to abolish DST but implementation has stalled. The US shifts clocks on the second Sunday in March and first Sunday in November. The UK shifts on the last Sunday in March and October. Note that some countries (India, China, Russia) do

International Date Line

The International Date Line runs roughly along the 180° meridian (with diversions for island nations). Crossing it westward adds a day; crossing eastward removes a day. This is why a flight from Los Angeles to Sydney crosses tomorrow, and why Samoa changed sides of the date line in 2011 to align itself with its main trading partners in Australia and New Zealand, skipping December 30, 2011 entirely — a date that never existed for that country.

Scheduling Across Time Zones

For international calls and meetings, always specify time zones explicitly (not just the city name, as large countries span multiple zones). Tools like Every Time Zone, World Time Buddy, or Google 'time in [city]' are reliable for current times. For business scheduling, early morning US East Coast overlaps with late afternoon UK — the most common working-hours overlap for transatlantic calls. US West Coast to UK requires someone working outside standard hours.