Time & Date
Time Zone Converter
Convert a date and local time between two cities, including minutes and daylight saving transitions.
When clocks change, and where they don't
About 70 countries observe some form of Daylight Saving Time (DST), affecting roughly a fifth of the world's population. Implementations vary in start and end dates, the hour at which clocks shift, the size of the shift, and whether the rule is national or regional.
Understanding Time Zones
What is UTC?
UTC (Coordinated Universal Time) is the global time standard from which all other time zones are offset. It replaced GMT (Greenwich Mean Time) in 1960, though the two are often used interchangeably in casual contexts. UTC does not observe Daylight Saving Time — it's a constant reference point.
How UTC offsets work
Time zones are expressed as UTC+ or UTC- offsets. New York is UTC-5 in winter (EST) and UTC-4 in summer (EDT). Tokyo is UTC+9 year-round (Japan doesn't observe DST). When it's noon UTC, it's 7 AM in New York (winter) and 9 PM in Tokyo simultaneously.
Daylight Saving Time complications
Over 70 countries observe some form of DST, shifting clocks forward in spring and back in fall. Not all countries follow the same schedule — the US, EU, and Australia have different DST start/end dates. During transition weekends, a time zone's UTC offset changes, which can cause confusion in scheduling across regions.
Time zone best practices for scheduling
When scheduling across time zones: always specify the time zone explicitly (say "3 PM EST" not just "3 PM"), use UTC for technical systems and APIs, and verify whether DST is in effect on the meeting date. The safest approach for international teams is to anchor on one reference time zone (often UTC or the host's local time).
Guide
How to use the Time Zone Converter
The Time Zone Converter helps you make a quick estimate, compare scenarios, and understand the numbers behind the result. It is designed for fast planning, with enough context to make the answer useful instead of just a number.
- Choose the starting date, ending date, time, or location values that define the interval.
- Check whether the calculator is using calendar days, business days, time zones, or live countdown timing.
- Use the result breakdown to confirm the date math before copying it into a schedule or plan.
Method
How this calculator works
It resolves a dated local time to an exact instant, then converts to the destination date and time. Missing local times are rejected; repeated times require an occurrence choice.
This calculator is useful for scheduling calls and comparing local times across cities.
Because assumptions matter, try a few values that represent optimistic, typical, and conservative cases.
Date and time results depend on calendar rules, local time zones, daylight saving changes, and the exact time selected.
Example
Worked example
2 p.m. in San Francisco in winter is 7 a.m. the next morning in Tokyo — a 17-hour gap. In summer the gap is 16 hours, because California observes daylight saving time and Japan does not. The converter applies these rules automatically for any date you pick.
FAQ
Common questions
What is the best time for a call between New York and London?
London is five hours ahead of New York for most of the year. The classic overlap is 9 a.m.–12 p.m. Eastern, which lands at 2–5 p.m. in London — late enough for New York to be at work, early enough for London not to be done.
Why does the hour difference between two cities change during the year?
Regions switch daylight saving time on different dates — the US in mid-March and early November, the EU in late March and late October — and some places (Japan, most of Arizona, India) never switch. For a few weeks a year the usual offset shifts by an hour, which is exactly the kind of mistake this converter prevents.
What information do I need for the Time Zone Converter?
You usually need source and destination city presets, source date, hour and minute, and an occurrence choice for repeated local times. You can change the inputs and recalculate as many times as needed.
How does the Time Zone Converter calculate the result?
It resolves a dated local time to an exact instant, then converts to the destination date and time. Missing local times are rejected; repeated times require an occurrence choice.
Are the results exact?
Date and time results depend on calendar rules, local time zones, daylight saving changes, and the exact time selected.
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