How to Convert Time Zones (Quick Guide)

Time zones exist because the Earth rotates, and noon should mean the sun is roughly overhead no matter where you stand. But that simple concept creates a web of offsets, half-hour zones, daylight saving shifts, and date-line crossings that trip up even experienced travelers and remote workers. This guide gives you a concrete system for converting between any two time zones without making mistakes.

UTC: The Universal Reference Point

Every time zone in the world is defined as an offset from Coordinated Universal Time (UTC). UTC is the modern successor to Greenwich Mean Time (GMT) and is measured at the Royal Observatory in Greenwich, London. The two are functionally identical for everyday use, though UTC is the technical standard.

UTC itself never changes. It doesn’t observe daylight saving time. That stability is exactly why it’s the global reference: if you know the UTC time, you can calculate the local time anywhere in the world by adding or subtracting the appropriate offset.

Example: If the current UTC time is 18:00 (6:00 PM), then:

New York (UTC-5): 18:00 - 5 = 1:00 PM
London (UTC+0): 6:00 PM
Tokyo (UTC+9): 18:00 + 9 = 3:00 AM the next day

Major Time Zone Offsets

Here is a reference table of the most commonly used time zones:

Abbreviation	Name	UTC Offset	Major Cities
HST	Hawaii Standard	UTC-10	Honolulu
AKST	Alaska Standard	UTC-9	Anchorage
PST	Pacific Standard	UTC-8	Los Angeles, Seattle, Vancouver
MST	Mountain Standard	UTC-7	Denver, Phoenix, Calgary
CST	Central Standard	UTC-6	Chicago, Dallas, Mexico City
EST	Eastern Standard	UTC-5	New York, Toronto, Miami
AST	Atlantic Standard	UTC-4	Halifax, San Juan
GMT/UTC	Greenwich Mean	UTC+0	London, Lisbon, Reykjavik
CET	Central European	UTC+1	Paris, Berlin, Rome, Madrid
EET	Eastern European	UTC+2	Athens, Helsinki, Cairo
MSK	Moscow Standard	UTC+3	Moscow, Istanbul
GST	Gulf Standard	UTC+4	Dubai, Abu Dhabi
IST	India Standard	UTC+5:30	Mumbai, Delhi, Bangalore
ICT	Indochina	UTC+7	Bangkok, Hanoi, Jakarta
CST	China Standard	UTC+8	Beijing, Shanghai, Taipei, Singapore
JST	Japan Standard	UTC+9	Tokyo, Seoul
AEST	Australian Eastern	UTC+10	Sydney, Melbourne
NZST	New Zealand Standard	UTC+12	Auckland, Wellington

Note that some abbreviations overlap (CST is used for both Central Standard Time in the US and China Standard Time). Always confirm which zone you mean by referencing the UTC offset.

How to Convert Between Two Zones

The formula is simple:

Target Time = Source Time - Source UTC Offset + Target UTC Offset

Or equivalently:

Target Time = Source Time + (Target Offset - Source Offset)

Example 1: EST to PST

You have a meeting at 3:00 PM EST (UTC-5) and need the PST (UTC-8) equivalent.

Difference: (-8) - (-5) = -3 hours
3:00 PM + (-3) = 12:00 PM PST

EST to PST is always a 3-hour subtraction, regardless of daylight saving, because both zones shift at the same time in the United States.

Example 2: EST to CET

A client in Berlin (CET, UTC+1) wants to know when your 10:00 AM EST is in their time.

Difference: (+1) - (-5) = +6 hours
10:00 AM + 6 = 4:00 PM CET

Example 3: PST to IST

Scheduling a call with a team in India (IST, UTC+5:30) at 9:00 AM PST (UTC-8).

Difference: (+5:30) - (-8) = +13:30 hours
9:00 AM + 13:30 = 10:30 PM IST

That 13.5-hour gap means there is almost no overlap during standard business hours. This is why many US-India teams schedule calls either early morning Pacific or late evening India time.

Use the Time Zone Converter to handle these calculations instantly, including daylight saving adjustments.

Daylight Saving Time Complications

Daylight saving time (DST) shifts clocks forward by one hour in spring and back by one hour in fall. This means the UTC offset for a given location changes twice per year.

United States DST schedule:

Spring forward: Second Sunday of March at 2:00 AM local time (clocks jump to 3:00 AM)
Fall back: First Sunday of November at 2:00 AM local time (clocks return to 1:00 AM)

During DST, the abbreviations and offsets change:

Standard	Offset	Daylight	Offset
EST	UTC-5	EDT	UTC-4
CST	UTC-6	CDT	UTC-5
MST	UTC-7	MDT	UTC-6
PST	UTC-8	PDT	UTC-7

Key complications:

Not all regions observe DST. Arizona (except the Navajo Nation), Hawaii, and most US territories stay on standard time year-round. Globally, most of Asia, Africa, and South America don’t use DST.
Dates differ by country. The EU switches on the last Sunday of March and the last Sunday of October. Australia switches in October and April (reversed seasons). This creates periods where the offset between two cities temporarily changes.
The gap or overlap problem. On the spring-forward night, 2:00 AM to 2:59 AM doesn’t exist. On the fall-back night, 1:00 AM to 1:59 AM happens twice. Scheduling events during these windows can cause confusion.

Pro tip: When scheduling recurring meetings across countries, pick a UTC time and let each participant convert to local. This avoids confusion when DST start dates differ between countries. Many calendar applications handle this automatically if the event is set in UTC.

The International Date Line

The International Date Line (IDL) runs roughly along the 180-degree meridian in the Pacific Ocean, with several zigzags to keep island nations on the same date. Crossing the date line changes the calendar date:

Traveling westward (e.g., from the US to Asia): Add one day.
Traveling eastward (e.g., from Asia to the US): Subtract one day.

This means two places can be at the same clock time but on different dates. For example, when it is 3:00 PM Tuesday in Fiji (UTC+12), it is 3:00 PM Monday in Hawaii (UTC-10) — same hour, different day, 22 hours apart in actual time.

For scheduling purposes, always include the date alongside the time and time zone when communicating across the date line.

Scheduling Meetings Across Time Zones

Finding a time that works for participants across multiple zones requires identifying the overlap window where everyone is within reasonable hours (roughly 8:00 AM to 8:00 PM).

Example: New York, London, and Tokyo

UTC	New York (EST)	London (GMT)	Tokyo (JST)
13:00	8:00 AM	1:00 PM	10:00 PM
14:00	9:00 AM	2:00 PM	11:00 PM
22:00	5:00 PM	10:00 PM	7:00 AM next day
23:00	6:00 PM	11:00 PM	8:00 AM next day

The table shows there is essentially no time during normal waking hours when all three cities overlap comfortably. The best compromise is usually 8:00-9:00 AM New York (1:00-2:00 PM London, 10:00-11:00 PM Tokyo) or rotating meeting times so no single group always gets the inconvenient slot.

Best Practices for Global Teams

Use UTC for all internal timestamps. Store event times, deadlines, and log entries in UTC. Convert to local time only when displaying to the user.
Specify the time zone explicitly. Write “3:00 PM EST” or “15:00 UTC,” never just “3:00 PM.” If your team spans multiple zones, default to UTC.
Use a shared world clock. Tools like the Time Zone Converter let you see multiple cities at once, eliminating mental math errors.
Account for DST transitions. Put a reminder on your calendar for the weeks when DST starts or ends. Check whether your recurring meetings have shifted by an hour.
Be specific with abbreviations. “CST” could mean Central Standard Time (UTC-6) or China Standard Time (UTC+8). When in doubt, state the UTC offset directly.
Record meetings for absent zones. If a meeting falls outside reasonable hours for some participants, record it and share the recording. Async communication tools bridge the gap when synchronous overlap is impossible.
Set up automated scheduling. Cron jobs and scheduled tasks should be defined in UTC. Use our Cron Expression Generator to build schedules that fire at the correct UTC time regardless of server location.

Frequently Asked Questions

What is the difference between UTC and GMT?

For all practical purposes, UTC and GMT represent the same time. GMT is the historical term based on solar observations at the Greenwich meridian in London. UTC is the modern standard maintained by atomic clocks worldwide. The difference between them is never more than 0.9 seconds (corrected by occasional leap seconds). Use UTC for technical work and international scheduling. GMT is still commonly used in British English and some airline timetables.

How do I remember which direction to add or subtract hours?

Think of the world map with UTC/GMT in the center (London). Zones to the east are ahead (positive offsets: +1, +2, … +12). Zones to the west are behind (negative offsets: -1, -2, … -12). Moving from a western zone to an eastern zone means adding hours. Moving from east to west means subtracting. A quick sanity check: when it is noon in New York, it should already be evening in Europe (later = east = add hours).

Why do some time zones have 30- or 45-minute offsets?

Not all governments chose to align with whole-hour offsets from UTC. India adopted UTC+5:30 as a compromise between its eastern and western extremes. Nepal uses UTC+5:45 to distinguish itself from India. The Chatham Islands (New Zealand) use UTC+12:45. Iran uses UTC+3:30. Afghanistan uses UTC+4:30. These fractional offsets make mental math harder, which is why a Time Zone Converter is especially useful when dealing with these regions.

How do I convert time zones for a date in the past or future?

Historical and future conversions are tricky because time zone rules change. Countries adopt, modify, or abandon daylight saving time. In 2011, Samoa jumped from UTC-11 to UTC+13, skipping an entire day. Russia has changed its DST policy multiple times. For historical dates, you need a time zone database (like the IANA/Olson database) that records every rule change. For future dates, use current rules but be aware they may change, especially if legislation is pending. Our Unix Timestamp Converter can help you convert specific timestamps to any time zone using the latest offset data.