Time Zone Converter
One clock, two fixed UTC offsets — the converted time, the day shift named, and the UTC instant both zones agree on.
Time Zone Converter
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Fixed offsets only — no DST schedule modeling
- Whole-minute resolution; no historical offset reforms
In short: 23:30 at UTC+5 is 03:30 at UTC+9 — the next day. The zones sit four hours apart, and both clocks agree on 18:30 UTC, the same day as the source. That is the whole mechanism: local time minus your offset is the instant, the instant plus the other offset is their clock, and the day rollover is named rather than hidden. Fixed offsets only — daylight saving is exactly the thing a fixed number cannot see.
Formula
target clock = source clock − source offset + target offset
The conversion runs through UTC because the instant is the one thing both zones share: subtract the source's offset to reach it, add the target's offset to leave. Offsets are fixed numbers you type — half-hour and quarter-hour zones included — and the day shift falls out of the arithmetic: a target past midnight is tomorrow, below zero is yesterday. Daylight saving is a zone changing its offset on schedule; a fixed-offset page does not model that shift, and says so.
Worked Example
- Enter the source clock and both UTC offsets.
- Read the converted clock and the day shift.
- Check the UTC line both zones agree on.
Defaults: 23:30 at UTC+5 to UTC+9 — 03:30 the next day, zones four hours apart, 18:30 UTC on the line. Reverse the offsets and the day runs backward.
Strengths & Limits Of This Model
Where this engine is strong
- Day shift named, not silent
- UTC line makes the arithmetic checkable
Where it stops
- You supply the offsets; seasonal shifts are on you
Practical Use Cases
Calls
what your evening is on their calendar
Travel
the arrival clock before the flight books
Half-hour zones
India at +5.5, Nepal at +5.75
Methodology & Editorial Standards
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Time Zone Converter — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
Why fixed offsets instead of named zones?
Because a named zone is a moving target: daylight saving rewrites the offset on legal schedule. This page converts between the numbers you type, which is exact arithmetic — and it says plainly that it cannot see a zone's seasonal shift. Look up today's offsets, then convert.
How do I handle daylight saving?
Use the offset in force on the date you mean. Most US zones run -5 in winter and -4 in summer; London runs 0 and +1. Convert with the winter pair or the summer pair — never one of each, or the answer absorbs an hour that belongs to a different date.
What are the half-hour and quarter-hour zones?
India runs at UTC+5:30, Nepal at UTC+5:45, parts of Australia at +9:30. Type 5.5 or 5.75 — the arithmetic is in minutes and lands exactly. The quarter-hour zones are the reason the input is free-entry rather than a dropdown of whole hours.
Where exactly does the day flip?
At the target's midnight. A conversion that lands past 24:00 reads as the next day; below 00:00 as the previous. The card names the shift, because a clock without its day is half an answer.
What is the UTC line for?
Checking. UTC is the instant both zones share, so it is the one clock that cannot disagree — if the two conversions do not round-trip through the same UTC minute, one of the offsets was mistyped. The page prints it so you can.
Can I convert 24-hour and 12-hour clocks?
The input is 24-hour HH:MM — 23:30, not 11:30 p.m. The 12-hour dressing is presentation; the arithmetic and the day shift are cleaner without ambiguity about which midnight is meant.
Why is my converted time an hour off from my phone?
Almost always daylight saving: the phone knows the zone's seasonal offset, the page uses the number typed. Enter the zone's current offset and the two agree exactly — which is the page's whole honesty: it converts what you give it, nothing behind your back.
Does the offset direction ever confuse the sign?
East of UTC is positive, west negative, and the formula subtracts the first before adding the second — which is why converting west can arrive 'before' you left. The gap card states which clock runs ahead, so the sign is visible, not silent.