Free calculator · Engineering
Find the working hours two time zones share
Pick your time zone and working day, then the other team's. The planner converts both to UTC for the date you choose, daylight saving included, and shows the hours you share, when they fall in each local time, and what moving the other team's day later would change.
How this is calculated
The planner turns each side's working day into an interval of real time (UTC) for the chosen date, using the IANA Time Zone Database through the browser's Intl.DateTimeFormat, and adds up where the intervals intersect.
Step by step
- Convert your working day on the chosen date from your local time to UTC. Daylight saving time is applied for that date; an end time at or before the start runs past midnight.
- Convert the other team's working day to UTC on their local dates the day before, the same day and the day after your date, so days that cross midnight are caught.
- Skip Saturdays and Sundays on either side, and report any overlap that a skipped weekend day would have added.
- Intersect your interval with each of the team's intervals and add the lengths. No minimum and no maximum: intervals that only touch add nothing.
- Show each shared window in both local times and UTC, with each side's UTC offset at the start of the window, and suggest the start of the longest window as a meeting time.
- Repeat the calculation with the other team's whole day moved 1, 2, 3 and 4 hours later to show shift scenarios.
Default assumptions
Assumptions marked adjustable can be changed in the calculator; the others are fixed parts of the model.
| Assumption | Default | Sources |
|---|---|---|
| Your time zoneadjustable | London (UK) (Europe/London) | |
| Your working day startsadjustable | 09:00 | None |
| Your working day endsadjustable | 17:30 | None |
| The other team's time zoneadjustable | Kolkata (India Standard Time) (Asia/Kolkata) | |
| The other team's day startsadjustable | 09:30 | None |
| The other team's day endsadjustable | 18:30 | None |
| Dateadjustable | 15 Jan 2026 |
What this doesn’t model
- Public holidays, leave and part-time patterns aren't modelled; every weekday is a working day.
- Weekends are Saturday and Sunday on both sides; countries with a different weekend aren't modelled.
- Time zone rules come from the copy of the IANA database built into your browser, which can lag a recent rule change.
- Shared hours on paper don't account for meetings, focus time or lunch breaks inside either working day.
- Shift scenarios are for discussion; shift patterns are agreed per engagement.
Sources
- Internet Assigned Numbers Authority (IANA), Time Zone Database. Accessed . The database of current and historical UTC offsets and daylight-saving rules. Release 2026e was published on 29 September 2026; your browser uses the copy built into it.
- Ecma International (TC39), ECMAScript Internationalization API Specification: time zone names. Accessed . Requires implementations of Intl.DateTimeFormat to use the IANA Time Zone Database for named time zones.
Last reviewed by the QuantmHill engineering team. Found an error?
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Frequently asked questions
Each working day is converted from local time to UTC for the date you pick, using the IANA time zone rules built into your browser. Your day is compared with the other team's days on the day before, the same day and the day after, and the shared time is added up. Nothing is rounded up or given a minimum: days that only touch share 0 hours.
Daylight saving time. The UK, Europe, most of the US and Canada, and south-eastern Australia move their clocks on different dates, while India, Singapore, Thailand and Japan don't. London and India share 4 hours of a standard day in January and 5 hours in July, for example.
India (UTC+5:30) is 4½–5½ hours ahead of the UK, 1½ hours behind Thailand, 2½ behind Singapore, 4½–5½ behind Sydney, and 9½–13½ ahead of the continental US. The ranges come from daylight saving time in the other country.
The India working day here is an example of standard hours, not a commitment. Working-hours overlap is agreed for each engagement and written into the statement of work — the shared window, who shifts hours, and how handoffs work outside it. The shift scenarios are there to help you decide what to ask for.
No. Saturdays and Sundays are treated as non-working days on both sides. If part of your day would overlap the other team's Saturday or Sunday, the planner leaves it out and says how much was skipped.
Yes. Add ?you= and &team= with IANA zone names to the page address, for example ?you=America/New_York&team=Asia/Kolkata, and optionally &date=2026-07-15. Unknown zones fall back to the defaults.
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