Why does the time difference between two cities change throughout the year?

If one or both zones observe daylight saving time and switch on different schedules, their relative offset shifts.

Where does the list of time zones come from?

From `Intl.supportedValuesOf('timeZone')`, exposing the browser's built-in IANA time-zone database.

What if my browser doesn't support that API?

The tool falls back to a curated list of major time zones — relevant only for unusually old browsers.

Why do some zones show offsets like UTC+5:30?

Several countries genuinely use half-hour or 45-minute UTC offsets (India +5:30, Nepal +5:45).

Does this work for past or future dates?

Yes — enter any date, and the tool computes the correct historical or scheduled-future DST status.

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Date & Age

Time Zone Difference Calculator

Compare the time in two zones for any date, DST-aware.

🔒 Runs entirely in your browser — nothing here is ever uploaded

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About the Time Zone Difference Calculator

Compares the wall-clock time in two time zones for any date, computing each zone's real UTC offset from the IANA time-zone database your browser ships with — so results are automatically DST-aware for any date they cover.

100% Free Runs in Your Browser No Sign-Up Required

How to use it

Choose Zone A and Zone B from the full list of IANA time zones.
Enter a date and time in Zone A.
Read the equivalent time in Zone B, both zones' UTC offsets, and the difference between them.

Formula

The entered wall-clock date/time in Zone A is converted to the actual UTC instant it represents. Each zone's offset from UTC is computed at that specific instant, so the difference automatically reflects whichever zone(s) are observing daylight saving time on that date.

Worked example

Comparing America/New_York and Asia/Kolkata for a summer date: New York observes Eastern Daylight Time (UTC−4) while Kolkata stays at a fixed UTC+5:30 year-round — a 9.5-hour difference, versus 10.5 hours in winter.

Interpreting your result

Time zone offsets aren't fixed — they change with daylight saving time, and not every zone observes DST. This tool computes offsets for the specific date/time you enter, using the browser's built-in IANA time-zone database.

Recommendations

• The same two zones can show a different hour difference in summer versus winter if either observes daylight saving time.
• Use 'Swap' to quickly flip which zone is being compared from which direction.
• Not every UTC+X:30 or +X:45 offset is a mistake — several countries genuinely use half-hour or 45-minute offsets from UTC.

Frequently asked questions

Yes — offsets are computed for the specific date and time you enter using the browser's IANA time-zone database.