Time & Dates
Converting between two zones
Both offsets are signed hours from UTC. Subtracting the source offset reaches UTC and adding the target offset leaves UTC, and the two steps compose into one line.
The Formula
target time = source time - source offset + target offset
Both offsets are signed hours from UTC. Subtracting the source offset reaches UTC and adding the target offset leaves UTC, and the two steps compose into one line.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| t_s | Source local time | time | The clock reading in the source zone. |
| o_s | Source offset | hours | Hours the source zone is ahead of UTC. |
| o_t | Target offset | hours | Hours the target zone is ahead of UTC. |
| t_t | Target local time | time | The clock reading in the target zone. |
What Each Symbol Means
t_stime
Source local time
The clock reading in the source zone.
o_shours
Source offset
Hours the source zone is ahead of UTC.
o_thours
Target offset
Hours the target zone is ahead of UTC.
t_ttime
Target local time
The clock reading in the target zone.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to convert time zones page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Convert Time Zones, filed under Everyday Life. Every number the guide produces comes from substituting into this one line.