Time Zone Converter
Convert times between different time zones instantly. Perfect for international meetings, travel planning, and remote work coordination. Automatically handles daylight saving time.
Reviewed by the Calcura editorial team · Last reviewed
- Question
- How do I convert a time between time zones?
- Answer
- Take the source time, convert to UTC by subtracting the source's UTC offset, then add the destination's UTC offset. For example, 3 PM in New York (UTC−5 in winter) is 3 − (−5) = 20:00 UTC, which in London (UTC+0) is 20:00 — 8 PM. Always use IANA time zones (like 'America/New_York') instead of abbreviations (EST) because they handle daylight saving automatically.
▸Show formula & caveatsHide formula & caveats
- Formula
target_time = UTC(source_time) + target_offset- Caveats
- DST rules change by country and year — the IANA tz database (tzdata) is authoritative.
- Time-zone abbreviations are ambiguous: CST can mean Central Standard Time, China Standard Time, or Cuba Standard Time.
- Meetings scheduled across DST transitions can jump — Europe and US don't change DST on the same date.
What This Calculator Does
This calculator converts a date and time from one IANA timezone to another, automatically applying the correct UTC offset including daylight saving time. It uses the browser's Intl.DateTimeFormat API, which reads from the IANA tz database — the same source of truth used by operating systems, databases, and programming language standard libraries. The result is the same instant in time, re-expressed in the destination timezone's wall-clock.
When To Use This Calculator
Scheduling an international meeting
A 10:00 New York meeting on 2026-04-18 converts to 15:00 London (UTC+1 BST, since UK DST has started). In January the same 10:00 NY converts to 15:00 London (UTC+0 GMT — because US DST hasn't started yet either).
Confirming a webinar start time
A vendor publishes '18:00 UTC' for a product launch. Convert to your local timezone before blocking the calendar — 18:00 UTC = 14:00 New York (EDT) or 19:00 London (BST) on 2026-04-18.
Coordinating deadlines across offices
A 'Friday 17:00 Pacific' filing deadline translates to Saturday 10:00 Tokyo (JST). Remote teammates need the converted deadline to avoid submitting after the cutoff.
Arranging calls with regions that don't observe DST
Arizona (UTC-7 year-round) and Phoenix don't follow Mountain DST. From March–November, Arizona aligns with Pacific Time, not Mountain Time — confirm before scheduling.
How It Works
The calculator uses IANA timezone identifiers (e.g., America/New_York, Europe/London) rather than abbreviations like EST or GMT, because abbreviations are ambiguous — IST means both India Standard Time and Irish Summer Time. Intl.DateTimeFormat looks up the UTC offset for the specified date in the tz database, which encodes the full history of DST rules per zone. The conversion is: source_local_time + source_offset = UTC = destination_local_time + destination_offset. Because the tz database is updated when governments change DST rules (e.g., Mexico ended most DST in 2022), results stay accurate for historical, present, and near-future dates.
Formula
UTC_instant = source_time − source_UTC_offset(date, zone)
destination_time = UTC_instant + destination_UTC_offset(date, zone)
offsets include DST if zone observes it on given dateReal-World Example
Scenario
A team in San Francisco wants to host a 09:00 PT standup on 2026-04-20 and needs converted times for colleagues in London, Berlin, Mumbai, and Sydney.
Calculation
Source: 2026-04-20 09:00 America/Los_Angeles (PDT, UTC−7) UTC: 16:00 London (BST, UTC+1): 17:00 Berlin (CEST, UTC+2): 18:00 Mumbai (IST, UTC+5:30): 21:30 Sydney (AEST, UTC+10): next day 02:00
Result
The standup rotates into Sydney's overnight hours — consider alternating meeting time, or record the session. Mumbai teammates get a 21:30 call that's workable but not ideal. The London/Berlin window is reasonable. Without the IDL-crossing check, Sydney participants might have assumed the same calendar day.
Common Mistakes to Avoid
Mistake: Using abbreviations instead of IANA zones
Solution: 'CST' means Central Standard Time (US) or China Standard Time (Asia). 'IST' means India Standard Time or Irish Summer Time. Use IANA names (America/Chicago, Asia/Shanghai, Asia/Kolkata, Europe/Dublin) to eliminate ambiguity.
Mistake: Assuming DST transitions align globally
Solution: US DST starts second Sunday in March; EU DST starts last Sunday in March. There's a ~2-week window each spring where US-Europe time differences are one hour off. The tz database handles this automatically; back-of-envelope math doesn't.
Mistake: Ignoring the International Date Line
Solution: Converting eastward past the IDL adds a day; westward subtracts one. A Monday 14:00 New York call is Tuesday 06:00 Tokyo — not Monday 06:00. The calculator shows the destination date; always check it when spanning >12 hours.
Mistake: Treating GMT and UTC as interchangeable year-round
Solution: GMT is the UK's winter time. In summer, the UK is on BST (UTC+1), not GMT. UTC is a time standard that never observes DST. 'London time' is GMT in January but BST in July.
Time Zone Converter vs. Related Calculators
Countdown Calculator
For counting down to an event at a specific moment — pair with this converter to first pin down the target time in your local timezone.
Date Difference Calculator
Returns the span between two dates in days/weeks/months. Doesn't handle timezone conversion — use this one first if timezones differ.
Workdays Calculator
Counts Mon–Fri workdays. Combine with timezone conversion when scheduling multi-region business deadlines.
When This Isn't the Right Tool
Historical dates before DST was standardized
Use instead: Pre-1970 DST rules are partially recorded in the tz database but not fully reliable. For 19th-century or early-20th-century conversions, consult historical timekeeping references rather than assuming modern rules.
Astronomical or scientific timekeeping
Use instead: Civil time (what this tool computes) differs from TAI and UT1 by leap seconds. For astronomy, GPS engineering, or precise scientific timing, use a TAI- or UT1-aware tool.
Religious calendar observances
Use instead: Sunset-based times (Shabbat, Ramadan fasting) depend on local sunrise/sunset, not just timezone offset. Use a prayer-time or sunset-aware tool, not a raw timezone converter.
Future dates where DST rules may change
Use instead: Governments occasionally alter DST rules (Mexico 2022, Lebanon 2023). Conversions years into the future use the tz database's current rules, which may not reflect legislation not yet enacted. For far-future scheduling, re-verify closer to the date.
How to Verify This Calculation
In Python, use zoneinfo.ZoneInfo and datetime.astimezone. In PostgreSQL, AT TIME ZONE handles conversions. Cross-check with timeanddate.com or worldtimebuddy.com for a visual confirmation. All three should agree to the minute.
Sources
- IANA Time Zone Database — Authoritative source for global timezone rules, including DST transitions and historical changes. Updated whenever governments alter timezone policy.
- ISO 8601 — Date and Time Format — International standard for representing dates, times, and UTC offsets in unambiguous form.
- BIPM — Coordinated Universal Time (UTC) — Bureau International des Poids et Mesures definition of UTC and its relationship to TAI and civil time.
Reviewed by the Calcura editorial team · Last reviewed