Time Zone Converter Units
Convert a time between any two zones, with daylight saving handled properly.
Time Zone Converter is a free online tool that convert a time between any two zones, with daylight saving handled properly. It runs entirely in your web browser using Intl, so files are processed on your own device and never uploaded to a server. There is no sign-up, no file size limit imposed by the site, no watermark and no paid tier.
- Price
- Free — no account, no quota, no watermark
- Category
- Units
- Where it runs
- In your browser, on your device
- Files uploaded
- None
- Technology
- Intl
- Settings
- 4
- Works offline
- Yes, after the first visit
About Time Zone Converter
This uses the browser’s own IANA time zone database through `Intl`, the same data your operating system carries, so daylight saving is applied as it actually was on the date you pick rather than as it is today. That distinction is not academic — several countries have changed or abolished their DST rules in recent years, and a converter built on a hard-coded offset table is silently wrong for months at a time. The offset is resolved twice internally, which is the standard way to avoid landing on the wrong side of a transition.
How to use it
- Enter date, time and from zone.
- Adjust the remaining 1 setting if the defaults do not fit your case.
The 4 settings
| Setting | What it does | Default |
|---|---|---|
| Date | Free text. | 2026-08-02 |
| Time | Free text. | 14:30 |
| From zone | Choose from 64: UTC, Europe — London, Europe — Dublin, Europe — Lisbon, Europe — Madrid, Europe — Paris…. | Europe — London |
| To zone | Choose from 64: UTC, Europe — London, Europe — Dublin, Europe — Lisbon, Europe — Madrid, Europe — Paris…. | America — New York |
Under the hood
| Runs on | Intl — handles locale-aware formatting |
| Controls | Date, Time, From zone, To zone |
Questions
Why is the offset different from what I expected?
Probably daylight saving. London is UTC+0 in winter and UTC+1 in summer; New York is UTC−5 and UTC−4. The gap between two zones is therefore not constant, and the two do not always switch on the same weekend — for a couple of weeks each spring the difference is an hour off its usual value.
What about times that do not exist?
When clocks go forward, an hour is skipped — 01:30 simply did not happen on that date in that zone. The result is normalized to a real instant rather than reporting an error, which is what most date libraries do, so treat an answer near a transition with care.
Why abbreviations like BST and EDT rather than fixed offsets?
Because abbreviations are ambiguous — CST is used for three different zones, and IST for three more. IANA names like `Europe/London` identify a place and its full history of rules, which is why every serious system stores those instead.