Meeting Planner

Scheduling a meeting across many people in many timezones is one of the unsung hard problems of modern remote work. The naive approach - everyone votes on a Doodle poll - falls apart with more than 4 timezones because most candidate slots land outside someone's business hours. Tools like When2Meet help, but require everyone to manually click their availability. This page is the structural opposite: each attendee declares only their timezone and business hours; the algorithm then computes the overlap automatically.

The optimal-meeting problem is a constrained search. Each attendee defines a per-day business window (typically 9 AM to 5 PM in their local timezone). The job is to find UTC hours where every attendee's local hour falls inside their window. With N attendees and 48 half-hour candidate slots per day, the brute-force search is 48 * N - trivial for any modern device. The clever part is presenting the result so the meeting organiser sees not just ‘yes/no’ for each slot but the per-attendee local time and any compromises required.

Indian Standard Time (UTC+5:30) is the trickiest single timezone for global meeting scheduling because of its half-hour offset, which breaks the every-hour grid that most calendar UIs assume. The Madras (now Chennai) Observatory chose 82.5 degrees east in 1906, giving UTC+5:30 - a single zone for a country 2,933 km wide. India considered DST during the 1962 Sino-Indian war and the 1971 Bangladesh war and rejected it both times. This page handles the half-hour correctly via the IANA TZDB.

Nepal (UTC+5:45) and the Chatham Islands of New Zealand (UTC+12:45 / +13:45) push the half-hour problem to a 45-minute problem. Iran (UTC+3:30 / +4:30), Afghanistan (UTC+4:30), Myanmar (UTC+6:30), the Cocos Islands (UTC+6:30), and Newfoundland (UTC-3:30 / -2:30) all use 30-minute offsets. The IANA TZDB encodes every such offset; the Intl.DateTimeFormat API used on this page reads it correctly. The grid render below is in 30-minute resolution.

Daylight Saving Time complicates multi-timezone scheduling because different countries shift on different dates. The US shifts on the second Sunday of March and the first Sunday of November. The EU shifts on the last Sunday of March and the last Sunday of October. Australia shifts in the opposite direction in October and April. New Zealand and the Chatham Islands shift in September and April. For most of the year, two-thirds of the world is in the ‘wrong’ DST state relative to North America - which is why this page evaluates DST at the specific candidate meeting date, not just ‘now’.

The IT services industry has produced a vocabulary for these compromises. The ‘Eastern shift’ (5 PM - 2 AM IST) overlaps with the US East Coast workday. The ‘Central shift’ (6 PM - 3 AM IST) overlaps with the US Central workday. The ‘UK shift’ (12 PM - 9 PM IST) overlaps with London business hours. The ‘Aus shift’ (5 AM - 2 PM IST) overlaps with Sydney. This page's overlap algorithm naturally finds these regimes once you add the attendees.

The IANA Time Zone Database (TZDB) was founded by Arthur David Olson at the National Institutes of Health in 1986 and is now maintained collaboratively at iana.org/time-zones. It encodes every DST rule change in every region since 1880 - the 1918 Standard Time Act, the 1942-1945 War Time period in the US, the 1986 amendments, the 2007 Energy Policy Act, the EU's repeated DST rule changes - and updates within weeks of any government change. Every modern browser ships a copy via the Intl API.