# Time Zone Difference Calculator

> Free time zone calculator. Convert a time in one city to another, see the exact hour difference, and check the current local time in both cities.

Pick two cities, a date and a time in the first city. The calculator converts it to the second city's time, shows the exact hour difference, and displays what time it is in both cities right now.

*Interactive tool: enter your values at https://toollantern.win/time-zone-difference-calculator/ and results update instantly in your browser.*

## How the conversion works

Enter a time as it would appear on a clock in city A, and the calculator finds the same absolute instant in city B. It first converts your wall-clock time to a single point in time (a Unix timestamp), then renders that instant on the clock of city B using the IANA time zone database built into your browser. The difference is the UTC offset of B minus the UTC offset of A at that exact instant.

## Worked example

City A: **New York**, 14:00 on Oct 10. City B: **Tokyo**.

- 14:00 in New York (EDT, UTC-4) is 18:00 UTC.

- 18:00 UTC is **03:00 the next day** in Tokyo (JST, UTC+9).

- Difference: +9 - (-4) = **+13 h**. Tokyo is ahead of New York.

Try Kolkata for a half-hour case: 14:00 in New York is **23:30 the same day** in Kolkata (IST, UTC+5:30), a difference of **+9 h:30**.

## Daylight saving time is handled automatically

Offsets are measured at the instant you picked, not from a fixed table, so the tool follows daylight saving changes. New York is UTC-5 in January and UTC-4 in July, and the calculator knows which one applies to your date. Cities without daylight saving, like Tokyo or Singapore, stay on the same offset all year.

## Why the difference can change over the year

Two cities can drift apart and back together as their daylight saving schedules change. The United States and Europe switch on different weekends, so for a few weeks each spring and autumn the difference between New York and London is 4 hours instead of the usual 5. Always convert for the actual date of your call or flight, not from a number you remembered.

## Frequently asked questions
### Why does the time difference between two cities change during the year?

Mostly daylight saving time. Regions start and end it on different dates, so for a few weeks the gap between them shifts by an hour. This calculator measures the offset at the exact date you pick.

### Does this calculator handle daylight saving time?

Yes. It computes each city's UTC offset at the instant you selected using your browser's time zone database, so spring forward and fall back are applied automatically.

### What time should I pick for a meeting across time zones?

Look for the overlap of normal working hours: 9:00 to 17:00 in each city. The converted time and the hour difference shown here tell you immediately whether a 14:00 start in New York means a 3:00 alarm in Tokyo.

### Is my data sent anywhere?

No. All conversions run in your browser with the time zone data it already has. Nothing you enter leaves your device.

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Interactive version: https://toollantern.win/time-zone-difference-calculator/