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overlap grid · 24h · DST-aware · live

Find overlapping work hours across timezones

Pick the zones for everyone on the call. The 24-hour grid colours cells where each zone is in working hours, and highlights the slots where everyone overlaps.

Meeting Planner
Zones
4
selected
Window
9–17
local h
Overlap
0h
none
Mode
DST-aware
client
Work hours–
input · zones
Active
output · 24h grid
Zone01234567891011121314151617181920212223
America/Los_Angeles UTC-07:0017181920212223012345678910111213141516
America/New_York UTC-04:0020212223012345678910111213141516171819
Europe/London UTC+01:0012345678910111213141516171819202122230
Asia/Tokyo UTC+09:0091011121314151617181920212223012345678
Overlap111111111111122222222111

Columns = UTC hour. Cells = local hour. Bottom row = how many zones are in-hours. Purple = everyone overlaps.

Quick Start

How the overlap grid works

For each UTC hour we project the local hour in every zone using its current offset. If it falls inside the work-day, the cell lights up. Overlap row counts zones with a match.

  1. 01

    Pick zones

    Add a zone for everyone joining the call.

    Parsing accepts ISO 8601, RFC 3339, RFC 2822, and Unix epoch seconds/milliseconds. The Date constructor handles the rest with browser-engine consistency.

    zonesISO 8601RFC 3339epochlive
    in · timestampIANA · ISO
    + Europe/Berlin
    loaded · ISO 8601zone · ready
  2. 02

    Set work window

    Default 9–17 — change to 8–18 or shift hours as you like.

    All math runs in UTC internally to avoid DST landmines; presentation converts back to the user’s zone via Intl.DateTimeFormat.

    windowUTC mathIntlDST-safelive
    win · optionsh · live
    9 – 17
    options applied · UTCDST-safe
  3. 03

    Read the grid

    Green = local time is inside the work day for that zone.

    Output respects the chosen timezone offset (Z vs +05:30) and pads digits per ISO conventions so sorts stay chronological.

    gridoffsetzone-awaresortablepadded
    cell · computedgreen · ready
    Tokyo 09 ✓
    computed · instantsortable
  4. 04

    Pick overlap

    Purple columns are the hours where everyone is in-hours.

    Copy writes via the Async Clipboard API; nothing pings a time server — the browser’s clock is the only oracle.

    overlapclipboardno oracledeterministicclient-side
    ✓ · copiedall · done
    14 UTC ⭐
    shipped · ready to shipsuccess
Pro tips

Time math without DST landmines

Always store UTC

Convert to local for display only. UTC storage avoids DST jumps and timezone drift in databases.

Watch leap seconds

POSIX time doesn’t count leap seconds; some systems do. Don’t use timestamps for sub-second precision across boundaries.

Prefer Temporal eventually

The Date API has many quirks. Temporal is shipping in modern engines and handles zones correctly.

Cron is timezone-tricky

Cron expressions run in the daemon’s local zone unless told otherwise. Pin a TZ explicitly for predictable runs.

ISO 8601 sorts naturally

YYYY-MM-DDTHH:mm:ss sorts correctly as a string. Don’t use US-style MM/DD/YYYY for anything machine-readable.

Beware Y2K38

Signed 32-bit Unix timestamps overflow in 2038. Use 64-bit storage end-to-end for long-lived systems.

Related toolsWorld ClockTZ ConverterTZ FinderUTC OffsetsDST CheckerISO Weeks
Use Cases

When to plan across zones

Distributed teams, sales, support.

All-hands

Find a slot tolerable for everyone in the company. Math runs in UTC under the hood to dodge DST jumps — local time is only for display. That means scheduling logic and date diffs survive March / November fall-back without the classic off-by-one-hour bug.

DST-safe

Customer calls

Schedule without making one side stay late. Browser clock is the only source — no external time server, no privacy leak, no rate limit. Pair with NTP-synced server time for high-accuracy use cases, but for human-scale work the browser clock is plenty.

UTC-correct

On-call handoff

Pick the moment with both engineers awake. ISO 8601 output sorts naturally as strings, perfect for filenames (report-2026-01-15.pdf) and log lines that need chronological ordering without parsing. Drop into S3 keys for free time-bucketing.

ISO-sortable

Pairing sessions

Two engineers, one window — eyeball it fast. Pairs cleanly with cron, scheduled tasks, and timestamped log analysis. The tool's output drops directly into APScheduler, Linux cron, or GitHub Actions schedule expressions without re-formatting.

spec-grade

Maintenance windows

Find quiet hours for your busiest regions. Output respects the chosen timezone offset (Z vs +05:30) so REST APIs and database TIMESTAMP WITH TIME ZONE columns round-trip cleanly. No ambiguity between "noon UTC" and "noon local".

zone-aware

Conferences

Pick streaming times that work globally. Confirms the difference between epoch seconds (10 digits) and milliseconds (13 digits) before you commit code that mis-multiplies by 1000 — a classic bug in cross-language time handling.

epoch-accurate
FAQ

Frequently asked questions

Yes — offsets are computed for today, so DST is already factored in.
Purple means every zone is in work hours at that UTC hour.
Supported. India and Newfoundland still render correctly.
Screenshot the grid — there's no PDF export yet.
No. All calculations run locally in your browser.
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