# Convert a time between time zones

Converts a time and date in one time zone to the time and date in another, with both UTC offsets and when the difference next changes.

- Page: https://www.acalculator.org/days/time-zone-converter
- JSON spec: https://www.acalculator.org/days/time-zone-converter.json
- Version: 482b055f0ad1

## Default answer

Example with the default inputs (Time 09:00, From New York (US Eastern), To London, UK, Date September 30, 2026) on the example date Wednesday, September 30, 2026: 9:00 AM on September 30, 2026 in New York (US Eastern) is 2:00 PM on Wednesday, September 30, 2026 in London, UK.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| at | Time | The clock time in the From zone. |
| from | From | The time zone of that time (IANA name). |
| to | To | The time zone to convert to (IANA name). |
| on | Date | The date in the From zone. Today, unless you change it. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| time | Time there | The clock time in the To zone at that moment. |
| date | Date there | The date in the To zone at that moment. |
| difference | The To zone is | How far the To zone’s clock is ahead of or behind the From zone’s clock at that moment. |
| fromZone | From zone | The From zone’s name, abbreviation, and UTC offset at that moment. |
| toZone | To zone | The To zone’s name, abbreviation, and UTC offset at that moment. |
| next | Difference changes next | The next difference and when it starts, in the From zone's local time, within 366 days. |

## Method

Find the instant (UTC) at which the From zone’s clocks show the date and time, then read the To zone’s clock at that instant; both offsets come from the browser’s IANA time zone data.

## Assumptions

- Zones are IANA tzdata names (tzdata 2026a); the browser supplies their offsets and daylight saving rules, so a rule change arrives with a browser update.
- A time that does not exist in the From zone (skipped when clocks spring forward) has no answer. A time that occurs twice (when clocks fall back) shows both results, earlier first, for every output that differs.
- The difference is the To zone’s UTC offset minus the From zone’s, as “3 hours ahead”, “9 hours 30 minutes behind”, or “the same time”.
- “Difference changes next” is the first moment after the typed time, within 366 days, at which the difference changes: the new difference, then that moment as the From zone’s local date and time (“2 hours ahead from Saturday, October 31, 2026, 11:00 PM”).
- Each zone shows its name and abbreviation from the browser’s Unicode CLDR English names (left out when CLDR has none), then its offset as UTC+hh:mm or UTC−hh:mm.
- Dates from 2000 to 2040 work.

## Worked examples

1. at = 09:00, from = America/New_York, to = Europe/London, on = 2026-07-01 gives time = 14:00, date = 2026-07-01, difference = 5 hours ahead, fromZone = Eastern Daylight Time (EDT), UTC−04:00, toZone = British Summer Time (BST), UTC+01:00, next = 4 hours ahead from Saturday, October 24, 2026, 9:00 PM. Source: IANA Time Zone Database, tzdata 2026a (https://www.iana.org/time-zones).
2. at = 18:00, from = America/New_York, to = Australia/Lord_Howe, on = 2026-12-01 gives time = 10:00, date = 2026-12-02, difference = 16 hours ahead, fromZone = Eastern Standard Time (EST), UTC−05:00, toZone = Lord Howe Daylight Time (LHDT), UTC+11:00, next = 15 hours ahead from Sunday, March 14, 2027, 3:00 AM. Source: IANA Time Zone Database, tzdata 2026a (https://www.iana.org/time-zones).

## FAQ

### How do I convert a time between time zones?

Take away the From zone’s UTC offset to get UTC, then add the To zone’s offset. For example, 9:00 AM in New York on July 1 is UTC−04:00, so 13:00 UTC; London is then UTC+01:00, so it is 2:00 PM there.

### What happens when the clocks change?

On the day clocks spring forward, an hour of local time is skipped (in the US, 2:00 AM to 2:59 AM), so a time in it does not exist and the converter says so. On the day they fall back, an hour happens twice (1:00 AM to 1:59 AM in the US), so the converter shows both results, earlier first.

### Why does the difference between two cities change during the year?

Because their clocks change on different dates, or only one of them changes. New York and London are 5 hours apart for most of the year but 4 hours apart for a few weeks in March and in October to November, because the US and Europe change on different Sundays.

### Where do the time zones come from?

From the IANA time zone database, as built into your browser. When a country changes its rules, the new rules arrive with a browser update, so the converter needs no update of its own.

## Sources

- IANA Time Zone Database, tzdata 2026a (https://www.iana.org/time-zones)