What is the difference between GMT and UTC?

Functionally the same for everyday use. UTC is the scientific standard based on atomic clocks; GMT is a time zone based on the prime meridian in Greenwich, England. The UK observes GMT in winter and BST (UTC+1) in summer.

What is DST and which countries use it?

Daylight Saving Time shifts clocks forward by 1 hour in spring to extend evening daylight. The US, EU, most of Australia, and Canada observe DST. Countries near the equator (India, China, much of Africa) do not — daylight hours vary little year-round.

How do I avoid time zone mistakes in scheduling software?

Always schedule in UTC or have participants specify their UTC offset. Prefer tools like Google Calendar that automatically adjust to each participant's local time zone. Avoid naming times by city (e.g. 'London time') without confirming whether DST is currently in effect.

What is the International Date Line?

The IDL is an imaginary line at roughly 180° longitude where the calendar date changes. Crossing it westward adds a day; crossing it eastward removes a day. This is why a flight from Los Angeles to Tokyo can 'lose' a day even though the flight is only ~11 hours.

Formula Guide

How to Convert Between Time Zones

Time zones define local time as an offset from Coordinated Universal Time (UTC). Most conversions involve adding or subtracting hours (and sometimes 30 or 45 minutes) from UTC. The complexity comes from Daylight Saving Time (DST), which shifts clocks by one hour in spring and reverts in autumn — and not all countries or regions observe it. For scheduling across borders, always confirm the current offset at the specific date rather than assuming a fixed offset.

Last updated: March 31, 2026

The Formula

Local Time = UTC Time + UTC Offset
Conversion: Time in Zone B = Time in Zone A − Offset A + Offset B

Common UTC offsets:
  UTC−8: US Pacific Standard Time (PST)
  UTC−5: US Eastern Standard Time (EST)
  UTC+0: London (GMT/UTC in winter)
  UTC+1: Central European Time (CET)
  UTC+5:30: India (IST) — no DST
  UTC+8: China Standard Time (CST) — no DST

Daylight Saving Time: US clocks spring forward 1 hour on the 2nd Sunday of March (EDT = UTC−4), and fall back on the 1st Sunday of November (EST = UTC−5).

Variable Definitions

Symbol	Name	Description
UTC	Coordinated Universal Time	The reference time standard — all time zones are expressed as offsets from UTC
Offset	UTC Offset	The number of hours (and sometimes minutes) added to or subtracted from UTC to get local time

Step-by-Step Example

Schedule a meeting at 3:00 PM Eastern Time (ET, UTC−5 in winter). What time is it in London (UTC+0), Berlin (UTC+1), and Mumbai (UTC+5:30)?

Given

Meeting time:3:00 PM ET (UTC−5)

Solution

1
Convert ET to UTC: 3:00 PM + 5 hrs = 8:00 PM UTC
2
London (UTC+0): 8:00 PM UTC + 0 = 8:00 PM GMT
3
Berlin (UTC+1): 8:00 PM UTC + 1 = 9:00 PM CET
4
Mumbai (UTC+5:30): 8:00 PM UTC + 5:30 = 1:30 AM IST (next day)

3 PM ET = 8 PM London = 9 PM Berlin = 1:30 AM Mumbai (next day).

Ready to calculate?

Use the free Timezone Converter — instant results, no sign-up.

Open Calculator

Common Mistakes to Avoid

Using a fixed offset without checking DST — Eastern Time is UTC−5 in winter (EST) and UTC−4 in summer (EDT); scheduling a meeting using the wrong offset shifts it by an hour.

Forgetting that not all countries observe DST — India, China, and Japan have no DST; their offset is constant year-round.

Crossing midnight without adjusting the date — a meeting at 8 PM UTC is the next calendar day for UTC+5:30 and beyond.

Confusing GMT and UTC — they are functionally equivalent for practical purposes, but UTC is the formal international standard.

Frequently Asked Questions

Related Guides

How to Convert Between Hourly, Monthly & Annual Salary

Salary Converter

How to Calculate the Cost of a Meeting

Meeting Cost Calculator