Timezone Comparator

Compare times across timezones. Click or drag to select a time, reorder rows, switch to week view.

How it works

Each timezone is a horizontal strip of 24 half-hour slots, color-coded by time of day. Business hours (9 AM – 5 PM) appear in green, night in dark blue, early morning in amber, evening in orange, and late night in purple. A vertical now-line marks the current time across all strips. Click or drag to select a meeting window — the selection highlights across every row so you can instantly see what time it is in each city.

Switch to Week view (W) to see 7 days at a glance. Business hours (9–17) are shown by default; toggle "All hours" for the full 24h heatmap. Drag the grip handle to reorder rows. Press N to add a new city, Esc to clear the selection.

When you select a time window, the summary shows the duration and whether it falls within business hours for each city. Use Copy times to get a formatted list of local times for every timezone, or Export .ics to create a calendar invite. Selected timezones and view mode are saved in the URL for sharing.

Overlap calculation methodology

The overlap algorithm iterates over all 24 UTC hours (0–23). For each hour, it converts to local time in every selected timezone using the browser's Intl.DateTimeFormat API, then checks whether the local hour falls within the 9:00–17:00 business range. An hour is counted as overlapping only if all timezones are simultaneously in business hours.

This approach correctly handles half-hour offsets (India at UTC+5:30, Nepal at UTC+5:45), fractional offsets (Chatham Islands at UTC+12:45), and DST transitions. The Intl API resolves the current offset for each timezone on the reference date, so the result is always accurate for today's rules. Historical offset changes (e.g., a country that abolished DST last year) are also reflected because the API uses the OS timezone database.

Daylight saving time

DST shifts can silently change your overlap window. When the US "springs forward" in March, New York moves from UTC-5 to UTC-4, shrinking the overlap with London by one hour until the UK follows three weeks later. In the fall, the reverse happens: the US "falls back" before Europe, temporarily expanding the gap.

The tool handles this automatically. The UTC offset shown next to each city name always reflects the current DST state. If you're scheduling a recurring meeting across timezones that observe DST on different dates (US, EU, Australia, none), check the week view around transition dates to see if your overlap shifts.

Not all timezones observe DST. Most of Africa, Asia, and South America stay on standard time year-round. Arizona (US) does not observe DST but neighboring Navajo Nation does. The IANA timezone database encodes all of these rules, and the tool inherits them through the browser's Intl API.

Common use cases

Remote standup scheduling. Distributed teams need a daily standup time that works for everyone. Add your team's cities, check the overlap, and pick the greenest slot. If there's no full overlap, the period indicators (early, evening) help you find the least inconvenient time.

Client calls across regions. If you're in New York scheduling a call with Tokyo and London, the overlap between all three is often just 1–2 hours. The tool shows exactly which hours work and whether anyone is outside business hours.

Travel planning. Add your home city and destination to visualize the time difference. The color-coding helps you understand jet lag — if it's 3 AM at home when you land, the night band makes that obvious. Use the week view to plan which days to schedule early or late meetings as you adjust.

Event coordination. Planning a global webinar or product launch? Add the cities of your audience, find the time that's reasonable for the most people, and export a calendar invite. Share the URL so attendees can see the time in their own timezone.

FAQ

How do I find overlapping business hours across timezones?

Add timezones with the search box (or press N). The color-coded grid shows business hours in green. The overlap summary below the strips tells you exactly which hours are shared across all selected timezones.

What counts as business hours?

9:00 AM to 5:00 PM local time in each timezone. Overlap is calculated where all timezones are simultaneously within this range.

How do I share my comparison?

Timezones are saved in the URL automatically. Copy and share the link. You can also select a meeting window and use "Copy times" to get a formatted list, or "Export .ics" to create a calendar invite.

Does it handle daylight saving time?

Yes. The Intl API handles DST transitions automatically. Offsets always reflect the current DST status. Check the week view around DST transition dates to see how your overlap window shifts.

How does the week view work?

Week view shows 7 days (Monday–Sunday) as color-coded blocks. By default only business hours (9–17) are shown for a compact overview. Toggle "All hours" to see the full 24h heatmap. Click or drag to select times across the week. Press W to toggle between day and week view.

How many timezones can I compare?

No hard limit. 3–6 works best for readability. Reorder rows by dragging the grip handle on the left.

What keyboard shortcuts are available?

N — add a new timezone. W — toggle day/week view. Esc — clear the selection.

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