Compare Times Between Any Two Cities

What Is a Time Zone?

A time zone is a region of the Earth that observes a uniform standard time for legal, commercial, and social purposes. Time zones are defined as offsets from Coordinated Universal Time (UTC), the primary time standard by which the world regulates clocks and time.

The Earth is divided into 24 primary time zones, each roughly 15 degrees of longitude wide (since 360 degrees ÷ 24 hours = 15 degrees per hour). However, in practice, time zone boundaries follow country and regional borders rather than strict lines of longitude, which is why the actual map of time zones is irregular.

UTC itself has no offset — it is the baseline. All other time zones are expressed as UTC+ or UTC−. For example, Stockholm is in the Central European Time zone (UTC+1 in winter, UTC+2 in summer), while Tokyo is in Japan Standard Time (UTC+9, year-round).

UTC Offsets: A Reference Guide for Major Cities

The following table shows the UTC offset for major cities around the world. Note that many countries observe Daylight Saving Time (DST), which shifts the clock forward by one hour during summer months.

City	Time Zone	UTC Offset (Winter)	UTC Offset (Summer)
London, UK	GMT / BST	UTC+0	UTC+1
Stockholm, Sweden	CET / CEST	UTC+1	UTC+2
Zurich, Switzerland	CET / CEST	UTC+1	UTC+2
Oslo, Norway	CET / CEST	UTC+1	UTC+2
Athens, Greece	EET / EEST	UTC+2	UTC+3
Moscow, Russia	MSK	UTC+3	UTC+3 (no DST)
Dubai, UAE	GST	UTC+4	UTC+4 (no DST)
Mumbai, India	IST	UTC+5:30	UTC+5:30 (no DST)
Singapore	SGT	UTC+8	UTC+8 (no DST)
Tokyo, Japan	JST	UTC+9	UTC+9 (no DST)
Sydney, Australia	AEST / AEDT	UTC+10	UTC+11
New York, USA	EST / EDT	UTC−5	UTC−4
Los Angeles, USA	PST / PDT	UTC−8	UTC−7
São Paulo, Brazil	BRT	UTC−3	UTC−3 (no DST)

Daylight Saving Time: Why Clocks Change Twice a Year

Daylight Saving Time (DST) is the practice of advancing clocks by one hour during the warmer months so that evening daylight lasts longer. The idea was first proposed by Benjamin Franklin in 1784 and was widely adopted during the First World War to conserve energy.

In the European Union, clocks move forward by one hour on the last Sunday of March and back by one hour on the last Sunday of October. In the United States, the change happens on the second Sunday of March and the first Sunday of November.

Not all countries observe DST. Japan, China, India, Russia, and most of Africa do not change their clocks, which means the time difference between these countries and DST-observing nations changes by one hour twice a year. This is an important consideration for international business scheduling.

How to Schedule International Meetings Across Time Zones

Scheduling meetings across multiple time zones is one of the most common practical uses of time zone knowledge. Here are the key principles:

• Always specify the time zone explicitly when communicating across borders. "Let's meet at 3pm" is ambiguous. "Let's meet at 3pm CET (UTC+1)" is not.
• Find the overlap window — the hours during which both parties are within normal working hours (typically 9am–6pm). For Stockholm and New York, the overlap is approximately 3pm–6pm Stockholm time (9am–12pm New York time).
• Account for DST transitions — if a recurring meeting is scheduled across time zones, the effective time can shift by one hour when one country changes its clocks and the other does not.
• Use UTC as a neutral reference for technical documentation, server logs, and API timestamps to avoid ambiguity entirely.

Common Time Zone Abbreviations Explained

Time zone abbreviations can be confusing because the same letters sometimes refer to different zones in different parts of the world. Here are the most commonly encountered abbreviations:

• UTC — Coordinated Universal Time. The global baseline. No offset.
• GMT — Greenwich Mean Time. Equivalent to UTC+0. Used in the UK in winter.
• CET — Central European Time (UTC+1). Used by most of continental Europe in winter.
• CEST — Central European Summer Time (UTC+2). Used by most of continental Europe in summer.
• EET — Eastern European Time (UTC+2). Used by Greece, Finland, and other eastern EU countries in winter.
• EST — Eastern Standard Time (UTC−5). Used by the US East Coast in winter.
• EDT — Eastern Daylight Time (UTC−4). Used by the US East Coast in summer.
• JST — Japan Standard Time (UTC+9). Japan does not observe DST.
• IST — India Standard Time (UTC+5:30). India does not observe DST and uses a half-hour offset.

The International Date Line

The International Date Line (IDL) is an imaginary line running roughly along the 180th meridian in the Pacific Ocean. When you cross it travelling westward, you advance one calendar day. When you cross it travelling eastward, you go back one calendar day.

This is why it is possible for two cities to be in the same moment of time but on different calendar dates. For example, when it is Sunday 11pm in Auckland, New Zealand (UTC+12), it is still Sunday 12pm in London (UTC+0) — but if you travel east from Auckland across the IDL, you arrive in Samoa where it is Saturday 11pm (UTC−11).

The IDL is not a perfectly straight line — it bends around island nations so that they do not have different dates on different parts of their territory.