Time Zone Converter
Shift clock time between UTC offsets with day change shown.
What it does
Meeting across zones needs offset math, not guesswork. Each zone is hours east of UTC, negative west and positive east. Converting subtracts the from offset to reach UTC, then adds the to offset to land in the target zone.
The tool above takes a 24 hour time plus two UTC offsets and returns converted time, hour shift, and day change. The defaults 12:00 from -5 to 0 match the worked example, so the page opens showing 17:00 same day.
Half hour zones work the same with decimals. India at +5.5 is 10.5 hours ahead of US Eastern at -5. Crossing midnight wraps the clock and reports +1 day or -1 day. A 23:30 UTC flight landing in +5.5 reads 05:00 next day.
Daylight saving is the catch. Offsets here are standard values you enter. When DST is active, enter the DST offset instead, such as -4 for EDT instead of -5 for EST./work calendars should note which offset was used.
This page shows the formula, one full hand checked example at 12:00 EST to UTC, a reference table, and practice checks that run through the tool.
How to use
- Type the local time in 24 hour form.
- Type the from UTC offset, negative west, positive east.
- Type the to UTC offset in the same form.
- Read Converted time as HH:MM on a 24 hour clock.
- Read Hour shift as to minus from.
- Read Day change for same day, +1 day, or -1 day.
Formula
- from
- Hours east of UTC at the start, e.g., -5.
- to
- Hours east of UTC at the target, e.g., 0.
- 1440
- Minutes per day for wrap math.
All math uses minutes to keep half hours exact. Day shift is floor of unwrapped target over 1440. Seconds are not entered here.
Worked example
Example: 12:00 at UTC-5 to UTC
Noon in New York standard time to UTC.
- Write 12:00 as 720 minutes, from -5, to 0.
- UTC: 720 minus (-300) = 1020 minutes.
- Target: 1020 + 0 = 1020 minutes.
- Clock: 1020 / 60 = 17, so 17:00.
- Shift: 0 minus (-5) = 5 h.
- Day: 1020 inside 0 to 1439, so same day.
Reference table
| Zone | UTC | Noon EST is |
|---|---|---|
| New York EST | -5 | 12:00 |
| London GMT | 0 | 17:00 |
| Paris CET | +1 | 18:00 |
| Mumbai IST | +5.5 | 22:30 |
| Tokyo JST | +9 | 02:00 next day |
Limits
- Standard offsets you enter. DST must be entered manually.
- No date line history here. Historical zone changes are ignored.
- Times only, no dates. Multi day trips need a date tool too.
- Half hours supported, quarter hours like +5.75 are rejected here.
Common mistakes
- Using EST -5 during EDT daylight when -4 applies.
- Flipping from and to, so shift sign reverses.
- Reading 17:00 as 7 PM without converting 24 hour clock.
- Forgetting +1 day when landing past midnight.
- Entering GMT+5 as -5. East is positive.
Try it yourself
Quick checks. Answers sit tucked under each question.
23:30 UTC to +5.5?
05:00, shift 5.5 h, +1 day.
08:15 at -8 to -5?
11:15, shift 3 h, same day.
Questions
How do I convert zones?
Subtract from offset to reach UTC, add to offset to land. Wrap mod 24 hours.
What is 12 EST in UTC?
17:00 same day.
Half hours?
Yes, step 0.5 supports +5.5 and +9.5.
DST?
Ignored. Enter the active offset, e.g., -4 for EDT.
Why +1 day?
Landing past midnight wraps to next calendar day.
East positive?
Yes. Hours east of UTC, so New York -5, Paris +1.