Every day, millions of people glance at a clock without thinking that behind the hands lies one of history’s most ingenious conventions: the idea that the whole planet can agree on what time it is. This guide tells how that happened, explains the difference between UTC, GMT and Brasília time and shows how Brazil came to have the four time zones it has today.
What is a time zone?
A time zone is a band of the Earth’s surface in which all clocks show the same official time. The Earth completes a full turn on its axis every 24 hours, which means it rotates 15 degrees of longitude per hour. In theory, then, the world would be split into 24 zones of 15 degrees each, numbered from the Greenwich meridian.
In practice, time zones follow politics and economics more than geometry. Countries and states pick the zone that best fits the life of their population, and the result is a map full of cut-outs: there are half-hour zones, 45-minute zones and offsets ranging from 12 hours behind to 14 hours ahead of UTC.
Before time zones: every town had its own time
Until the 19th century, time was local. Noon was the moment the Sun reached its highest point in the sky, and each town set its clocks by it. Because the Sun reaches different places at different moments, two towns a few dozen kilometres apart already had slightly different times. As long as travel was done on horseback, nobody cared.
Railways changed everything. A single line could cross dozens of “local times”, and building a timetable without causing accidents or confusion became a nightmare. On November 18, 1883, US and Canadian railroads adopted standard time zones, a date remembered in the US as “the day of two noons”, because in many cities clocks were reset and noon happened twice.
The following year, in 1884, the International Meridian Conference in Washington chose the meridian that passes through the Royal Observatory at Greenwich, in London, as the world reference for longitude and time. Time zones have been counted from it ever since. Brazil followed the movement: a 1913 decree established the country’s official time zones, in force from 1914.
UTC, GMT and legal time: what is the difference?
GMT (Greenwich Mean Time) came from observing the Sun and the Earth’s rotation at the Greenwich Observatory. UTC (Coordinated Universal Time) is today’s standard: it is measured by extremely precise atomic clocks and occasionally receives a “leap second” so it does not drift too far from the Earth’s irregular rotation. In 2022 the General Conference on Weights and Measures decided to abandon leap seconds by 2035. In everyday life UTC and GMT show the same time, which is why time zones are written as “UTC-3” or “GMT-3”.
Each country defines its own legal time by law. In Brazil, the Brazilian Legal Time is kept by the National Observatory in Rio de Janeiro using atomic clocks, and “Brasília time” is the popular name for the country’s official time: UTC-3. The name refers to the federal capital and became a synonym for the correct time across the whole national territory.
Brazil’s four time zones
Brazil stretches more than 4,000 kilometres from east to west, which fits four time zones. Here is how they are distributed and what time it is in each right now:
| Zone | Where it applies | Time now |
|---|---|---|
| UTC-2 1 hour ahead of Brasília | Fernando de Noronha, Rocas Atoll, Trindade and Martim Vaz, Saint Peter and Saint Paul Archipelago | 21:14:54 |
| UTC-3 Brasília time | SP, RJ, MG, ES, DF, GO, BA, SE, AL, PE (except Noronha), PB, RN, CE, PI, MA, PA, AP, TO, PR, SC and RS | 20:14:54 |
| UTC-4 1 hour behind | AM (most of the state), MT, MS, RO and RR | 19:14:54 |
| UTC-5 2 hours behind | AC and southwestern AM | 18:14:54 |
It has not always been this way. In 2008 the country went from four zones to three, and Acre and southwestern Amazonas moved to UTC-4. In 2013 a law restored UTC-5 for that region and Brazil went back to four zones. For the current time in each state, see the list of Brazilian states.
Daylight saving time: a back-and-forth story
Brazil first adopted daylight saving time in the 1930s and used it on and off for decades. From the mid-1980s it was applied almost every year, usually between October and February, in the South, Southeast and Central-West regions. The idea was to make better use of daylight in the late afternoon and reduce electricity consumption at peak hours.
In April 2019 a federal decree abolished daylight saving time. The government justified the measure by saying the benefit to the power system had shrunk over the years. The last period ended in February 2019, and since then Brazilian clocks have been the same all year. In practice this made the maths simpler: the gaps between Brazilian time zones are fixed, and the only variation comes when talking to countries that still change their clocks, such as the United States and much of Europe. See which countries do in our daylight saving time guide.
Time zone curiosities around the world
- China: uses a single time zone, UTC+8, across a territory that would geographically span about five zones.
- India and Nepal: India uses UTC+5:30 and Nepal UTC+5:45. The Chatham Islands in New Zealand use UTC+12:45.
- Kiribati: the Line Islands use UTC+14, the most advanced time zone on the planet, and are among the first places to see a new day.
- Samoa: in 2011 the country moved to the other side of the International Date Line and “skipped” December 30, going straight from the 29th to the 31st.
- Russia: has 11 time zones, the most of any country with contiguous territory.
- France: because of its overseas territories, it is the country with the most time zones, more than a dozen.
- Spain: uses Central European Time even though it is geographically close to the Greenwich meridian; mainland Portugal uses Lisbon time, one hour behind.
- International Date Line: roughly follows the 180-degree meridian, with detours to respect borders. Crossing it moves the calendar forward or back by one day.
How to calculate the time difference
- Find the UTC offset of both places. Brasília is UTC-3.
- Subtract the origin offset from the destination offset: difference = destination UTC − origin UTC.
- Add the difference to the origin time. If it passes 24:00 it is the next day; if it goes negative it is the previous day.
Example 1: it is 15:00 in Brasília (UTC-3) and you want the time in Tokyo (UTC+9). Difference: 9 − (−3) = 12 hours. In Tokyo it is 03:00 the next day.
Example 2: in October, Lisbon is on UTC+1 (European summer time). Difference: 1 − (−3) = 4 hours. If it is 15:00 in Brasília, it is 19:00 in Lisbon. In European winter, Lisbon goes back to UTC+0 and the difference drops to 3 hours.
The extra care is the other country’s daylight saving time. To avoid mistakes, use the world time table, which already applies the rule in force for each zone, or plan with the meeting planner.