Timezone Offset Calculator
Convert a local time from one timezone to another by entering UTC offsets and the departure hour. Perfect for scheduling international calls, flights, or remote meetings across time zones.
About this calculator
Every timezone is defined by its offset from Coordinated Universal Time (UTC), expressed in whole or half hours. To convert a time from one timezone to another, you add the difference between the destination and origin offsets to the original time. The formula used is: destinationTime = ((timeHour + (timezone2 − timezone1)) + 24) mod 24. Adding 24 before applying the modulo ensures the result stays within the valid 0–23 hour range even when crossing midnight backwards. For example, UTC−5 to UTC+1 adds 6 hours to the local time. This approach works for all standard integer-offset timezones; half-hour and quarter-hour offsets (e.g., India UTC+5:30) require decimal inputs.
How to use
Suppose it is 15:00 (3 PM) in New York (UTC−5) and you want to know the time in Paris (UTC+1). Enter timeHour = 15, timezone1 = −5, timezone2 = 1. The calculator computes: destinationTime = ((15 + (1 − (−5))) + 24) % 24 = ((15 + 6) + 24) % 24 = 45 % 24 = 21. The result is 21:00 (9 PM) in Paris. This correctly reflects the 6-hour difference between Eastern Standard Time and Central European Time.
Frequently asked questions
How do I calculate the time difference between two time zones manually?
Subtract the origin UTC offset from the destination UTC offset to get the hour difference, then add that to your local time. If the result exceeds 23, subtract 24; if it falls below 0, add 24. For example, going from UTC+9 (Tokyo) to UTC−8 (Los Angeles) gives a difference of −17 hours. A meeting at 10:00 in Tokyo would be at 10 + (−17) = −7, which wraps to 17:00 the previous day in Los Angeles. Using the formula in this calculator automates this wrapping automatically.
What does UTC offset mean and how does it affect time zone conversions?
UTC offset is the number of hours (and sometimes minutes) that a timezone differs from Coordinated Universal Time, the global time standard. Positive offsets (e.g., UTC+5) are east of the prime meridian, while negative offsets (e.g., UTC−6) are west. When converting times, only the difference between the two offsets matters. Daylight saving time changes the offset temporarily, so you must use the correct seasonal offset for accurate results.
Why does the timezone calculator add 24 before using modulo 24?
The modulo operation returns the remainder after division, keeping the result in the 0–23 range that represents a valid hour in a 24-hour clock. Without adding 24 first, a negative result — such as when converting from a positive to a large negative offset — would remain negative, which is not a valid clock hour. Adding 24 ensures the value is positive before the modulo is applied, correctly wrapping times that cross midnight backwards. This is a standard programming technique for circular arithmetic on clock values.