Time Zone Offset Converter
A time zone offset is how far a local clock runs ahead of or behind Coordinated Universal Time, and converting between zones means adjusting for the difference between two offsets. This converter takes a clock time and the UTC offset where it applies, converts to UTC, then applies the target offset to give the corresponding local time elsewhere, reporting any day rollover when crossing midnight. Because daylight saving rules differ by date and place, you supply the offsets that are actually in effect rather than relying on a fixed zone, keeping the result correct for your specific date.
Time zone conversion formula
source decimal hours = hour + minute / 60
utc hours = source hours - source offset
target hours = utc hours + target offset
day change = floor(target hours / 24)
target clock = target hours mod 24
Subtracting the source offset gives UTC; adding the target offset gives the destination clock. The day change tells you if the result lands on the previous day (negative) or a later day (positive) after wrapping around 24 hours.
Offset notes
- Enter offsets in decimal hours: 5.5 means plus 5 hours 30 minutes.
- Use negative offsets for zones west of UTC, such as -5 for US Eastern Standard Time.
- Apply the daylight saving offset yourself when summer time is in effect.
- The IANA Time Zone Database is the authoritative record of zone offsets.
- A day change of +1 means the target time is on the following calendar day.
Time zone offsets: frequently asked questions
What is a UTC offset?
A UTC offset is the number of hours and minutes a local clock runs ahead of or behind Coordinated Universal Time. For example, US Eastern Standard Time is UTC minus 5 hours, written as -5, and India is UTC plus 5 hours 30 minutes, written as +5.5. Daylight saving time changes the offset seasonally.
How does this converter work?
It first converts the source local time to UTC by subtracting the source offset, then adds the target offset to get the target local time. Any whole days gained or lost in the process are reported as a day-rollover figure, so a late-evening time can correctly land on the next or previous day.
Why do I enter the offsets myself?
Because daylight saving rules and political changes to time zones vary by location and date, hardcoding a fixed offset for a named zone would risk being wrong. Entering the actual offset that applies on your date keeps the result accurate. The IANA Time Zone Database is the authoritative source for current offsets.
How are half-hour and quarter-hour zones handled?
Enter the offset as a decimal: 5.5 for plus five hours thirty minutes, or -3.5 for minus three hours thirty minutes. Some zones such as Nepal use 5.75. The converter works in decimal hours throughout, so any fractional offset is handled exactly.
Does this account for daylight saving time?
Not automatically. You supply the offsets that are actually in effect for your chosen date, including any daylight saving adjustment. If a region is observing summer time, use the summer offset; the converter then computes the correct corresponding time in the other zone.
Official sources
- Internet Assigned Numbers Authority: Time Zone Database.
- NIST Time and Frequency Division: Daylight Saving Time.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.