Time Zone Calculator
Convert a date and time between cities and see the time difference and any date change.
How it works
Choose the city you are starting from and the city you want, then enter the date and time in the first city. The calculator turns that wall-clock time into a UTC moment using the offset in force on that date, then shows the same moment in the second city.
UTC time = local time − offset of the first city
Time in second city = UTC time + offset of the second city
Difference = offset of second city − offset of first cityExample
10:00 on 15 January 2025 in Kolkata (UTC+05:30) is 04:30 UTC. New York is UTC-05:00 in January, so it is 23:30 on 14 January there. New York is 10 h 30 min behind Kolkata, and the date moves to the previous day (−1).
Common mistakes
- Using a fixed offset all year. The gap between two cities can change when one of them changes its clocks, so always check the date you actually mean.
- Reading EST or IST as a unique zone. Abbreviations such as IST are shared by several countries, which is why this tool asks for a city.
- Scheduling at a changeover hour. A time like 02:30 on the night clocks go forward does not exist, and one on the night they go back happens twice.
About this calculator
Pick two cities, a date and a time in the first one, and the calculator shows the same moment in the second: the local time, the time difference, whether the second city is ahead or behind, and whether the date moves a day forward or back.
It uses IANA time zone data through your browser, with the UTC offset read for the date you choose, so daylight saving is applied only when it is in force on that day and the difference can change during the year. The city list is a fixed selection of major cities. If a time does not exist because clocks skip forward, or happens twice because they go back, the result says so. Dates from 1970 to 2100 are supported.
Frequently asked questions
How does it handle daylight saving time?
The UTC offset of each city is read from the IANA time zone rules for the date you choose. New York is UTC-05:00 in January and UTC-04:00 in July, so the difference to a city without daylight saving, such as Kolkata, changes by an hour between those dates.
What does it mean when a time does not exist?
When clocks skip forward, some local times never occur, for example 02:30 on 9 March 2025 in New York. The calculator uses the first valid time after the shift (03:30 there) and tells you it did.
What if the time happens twice?
When clocks go back, a local time such as 01:30 on 2 November 2025 in New York occurs twice. The calculator uses the first occurrence and shows what the second one would convert to.
Is the result as accurate as an official time source?
It is as accurate as the time zone data in your browser. A country can change its rules at short notice, and a browser that has not been updated may not know about that yet. For a critical booking, confirm with the organiser.