What is the difference between UTC and GMT?

UTC (Coordinated Universal Time) is the modern technical standard based on atomic clocks. GMT (Greenwich Mean Time) is the historical standard based on Earth's rotation. In practice they show the same clock (UTC+0), but UTC has been the official reference since 1972.

How many time zones are there in the world?

There are 24 main zones, one per 15° band of longitude. Counting non-integer offsets (like India's UTC+5:30 or Nepal's UTC+5:45) and daylight saving, more than 40 distinct offsets are in use at the same time.

What time zone is Brazil in relative to UTC?

Brasília is at UTC-3 year-round. Brazil has four zones: Fernando de Noronha (UTC-2), Brasília (UTC-3), Manaus (UTC-4), and Acre (UTC-5).

Why do some countries have half-hour offsets?

For political and geographical reasons. India, Iran, Afghanistan, Myanmar, and Nepal chose offsets like UTC+5:30 or UTC+5:45 to better match the sun's position over their territory, instead of using a whole-hour multiple.

What is UTC? World time zones explained

May 2026

You've probably seen labels like UTC-3, UTC+1, or GMT on websites, flight tickets, or international emails. But what exactly is UTC, why is it the world's reference, and how does it differ from GMT? This article explains everything in plain terms — and shows how the concept affects your daily life.

What does UTC mean?

UTC stands for Coordinated Universal Time. It is the reference time standard used worldwide to define every time zone. Each zone is described as an offset relative to UTC — positive or negative.

For example: Brazil's Brasília is at UTC-3, meaning 3 hours behind UTC. Tokyo is at UTC+9, meaning 9 hours ahead of UTC.

Why UTC and not GMT?

GMT — Greenwich Mean Time — is the time at the Greenwich meridian in London, and was historically the world's time standard. UTC replaced GMT as the technical reference in 1972.

In practice, UTC and GMT show the same clock (both correspond to UTC+0). The difference is technical: GMT is based on Earth's rotation, while UTC is maintained by extremely precise atomic clocks and occasionally adjusted with 'leap seconds' to stay aligned with Earth's rotation.

How world time zones work

Earth takes 24 hours to complete a rotation. To keep noon roughly aligned with the sun overhead everywhere, the planet was divided into 24 time zones, each spanning 15 degrees of longitude.

In practice, zone borders don't follow straight lines — they bend around political boundaries. That's why an entire country (like Argentina or China) may use a single zone even when stretching far east to west.

Examples of zones around the world

UTC-10 — Honolulu (Hawaii)
UTC-8 — Los Angeles, Seattle, San Francisco
UTC-5 — New York, Toronto, Lima, Bogotá
UTC-3 — Brasília, Buenos Aires, Montevideo, Santiago (Chilean winter)
UTC+0 — London, Lisbon, Bissau, São Tomé
UTC+1 — Paris, Madrid, Berlin, Luanda
UTC+2 — Athens, Helsinki, Maputo, Cairo
UTC+3 — Moscow, Istanbul, Riyadh
UTC+5:30 — New Delhi (non-integer offset!)
UTC+8 — Beijing, Singapore, Manila, Perth
UTC+9 — Tokyo, Seoul
UTC+10 — Sydney, Brisbane
UTC+12 — Auckland (NZ winter)

Non-integer offsets: India, Iran, Nepal

Some countries use offsets that aren't exact multiples of an hour. The best known:

India: UTC+5:30
Iran: UTC+3:30
Afghanistan: UTC+4:30
Nepal: UTC+5:45 (the most unusual in the world)
Myanmar: UTC+6:30

Daylight saving shifts the offset

Many countries add 1 hour to their zone for part of the year. Lisbon alternates between UTC+0 (winter) and UTC+1 (summer). New York alternates between UTC-5 and UTC-4. When reading an offset, always check whether it refers to standard or daylight time.

What UTC is used for in daily life

Aviation: international flights use UTC to avoid confusion across zones.
Servers and databases: software and logs are stored in UTC for consistency.
International meetings: scheduling at '14:00 UTC' avoids ambiguity.
Sports events and broadcasts: times are often announced in UTC.

How to convert UTC to your local time

Just add or subtract your zone's offset. If you're in Brasília (UTC-3) and an event starts at 18:00 UTC, that's 15:00 Brasília time. In London winter (UTC+0), it's 18:00. In summer (UTC+1), it's 19:00.

Or use QueHoras, which converts automatically for any city in the world — always with DST correctly applied.

Frequently asked questions

What is the difference between UTC and GMT?: UTC (Coordinated Universal Time) is the modern technical standard based on atomic clocks. GMT (Greenwich Mean Time) is the historical standard based on Earth's rotation. In practice they show the same clock (UTC+0), but UTC has been the official reference since 1972.
How many time zones are there in the world?: There are 24 main zones, one per 15° band of longitude. Counting non-integer offsets (like India's UTC+5:30 or Nepal's UTC+5:45) and daylight saving, more than 40 distinct offsets are in use at the same time.
What time zone is Brazil in relative to UTC?: Brasília is at UTC-3 year-round. Brazil has four zones: Fernando de Noronha (UTC-2), Brasília (UTC-3), Manaus (UTC-4), and Acre (UTC-5).
Why do some countries have half-hour offsets?: For political and geographical reasons. India, Iran, Afghanistan, Myanmar, and Nepal chose offsets like UTC+5:30 or UTC+5:45 to better match the sun's position over their territory, instead of using a whole-hour multiple.