How To Convert Time Zones Calculator
A time zone conversion is two arithmetic steps around a shared reference. The day shift that comes out of it is the part people get wrong, not the arithmetic.
Time in New York
01:30 (same day)
- Time difference
- -13 hours
- Coordinated Universal Time
- 06:30 (same day)
- Source offset in use
- UTC+8 Shanghai
- Target offset in use
- UTC-5 New York
Offsets shown are standard-time offsets. Tick the summer-time boxes where it is in effect, because start and end dates differ each year.
The formula this calculator uses
target local time = local time - source offset + target offset
- t_s
- Local time in the source zone
- o_s
- UTC offset of the source zone, in hours
- o_t
- UTC offset of the target zone, in hours
- t_t
- Local time in the target zone
How to check the result by hand
- 1
Write down both offsets
Read the offset for each zone, including any summer-time hour. Both are signed, and UTC+8 is a larger offset than UTC+5:30 by two and a half hours.
- 2
Convert the local time to UTC
Subtract the source offset from the local clock. Fourteen thirty at UTC+8 becomes six thirty UTC, and the result can be negative or beyond a day.
- 3
Add the target offset
Add the target offset to the UTC figure. Six thirty UTC plus UTC-5 becomes one thirty, which is on the same day because the sum stayed positive.
- 4
Take the day shift
Divide the destination minutes by 1440 and take the floor. A -1 means the destination fell on the previous day and a +1 means the next one.
- 5
Check the difference the other way
The gap between the two clocks is one offset minus the other. Quoting it in the right direction is what makes a meeting invitation unambiguous.
For worked examples, common mistakes and the limits of this formula, read the full How To Convert Time Zones page.