Meeting Planner

Scheduling a meeting across time zones is deceptively difficult, and not because the arithmetic is hard — it's because the arithmetic keeps changing. A fixed "UTC offset" for a city is only true for part of the year in any region that observes Daylight Saving Time (DST): New York sits at UTC−5 in January and UTC−4 in July, and the exact date each region switches over is set independently by each country's own government, so the offset between any two DST-observing cities can shift not just twice a year but briefly by a different amount than usual during the one-to-three-week windows where one region has already changed clocks and the other hasn't. A calculator that hard-codes "New York is 5 hours behind London" will be quietly wrong for roughly two months of every year. This tool sidesteps that entire class of bug by never hard-coding an offset at all. Instead, it anchors on a single moment in time — the date and hour you choose, interpreted in your own browser's local time zone — and asks the browser's built-in internationalisation engine (the Intl.DateTimeFormat API, backed by the same IANA time zone database used by operating systems, phones, and every major scheduling tool) to render that exact moment in each participant's time zone. Because the browser resolves the correct offset for that specific date, DST transitions, historical rule changes, and even the odd 30- or 45-minute offsets used by a handful of countries are all handled correctly and automatically, without this tool needing to know any of those rules itself. The business-hours classification follows a simple, deliberately conservative rule of thumb: a participant's local hour between 9am and 5pm (9–17 in 24-hour terms) is marked as business hours, 6–9am and 6–10pm are marked as an early or late window that's workable but not ideal, and everything else — the small hours of the morning through to just before 6am, and from 10pm onward — is marked as unsociable hours. These bands are a general-purpose default, not a universal standard; actual working culture varies by company, country, and individual, so treat the colour coding as a fast visual filter for the obviously-bad slots rather than a precise rule for any specific team. The date the tool asks for is always the date in your own time zone, not a shared "UTC date" — this matters because the same instant in time can fall on two different calendar dates depending on where in the world you are (for instance, 9pm in Los Angeles is already the following morning in Tokyo). Rather than asking you to reason about that shift yourself, the tool lets you set the date and time exactly as you'd say them out loud ("Tuesday at 9am, my time") and handles the date-line and time zone translation for every other participant automatically, including flagging when their equivalent moment falls on a different weekday than yours.