Time looks simple until more than one place is involved. Offsets change twice a year in some countries and never in others, the changes happen on different dates on each side of the Atlantic, and a few places use half-hour or quarter-hour offsets. The time tools here use the time-zone database built into your browser — the same IANA database operating systems use — so they follow the official rules rather than a hard-coded table of offsets that goes stale.
The hours that do not exist
On the night clocks go forward, one hour of local time is skipped; on the night they go back, one hour happens twice. A meeting booked for 2:30 a.m. on the wrong Sunday either does not exist or is ambiguous. The time zone converter detects both cases and says so explicitly instead of silently picking a time, and the meeting planner highlights the weeks when the gap between two cities is different from usual — the most common reason a regular call starts an hour early for half the attendees.
Timers that stay accurate in the background
Browsers slow down timers in tabs you are not looking at to save battery. A countdown that adds one second per tick will drift by minutes. The countdown and focus timers here always compute the remaining time from the target moment and the current clock, so switching tabs, locking the screen or putting a laptop to sleep does not make them wrong when you come back. Alerts use a short tone generated in the page and, if you allow it, a system notification.
- Time zone converter: any time in several cities at once, with a 24-hour grid that shows everyone's working hours.
- Countdown timer: to a date and time or for a duration, with a shareable link.
- Pomodoro timer: work and break cycles with configurable lengths and a daily tally.
Settings such as your list of cities and your preferred session lengths are kept in this browser only, so they are there next time without any account.
Meetings across time zones
Scheduling across cities has three traps: there may be no hour when everyone is working, the usual gap between two cities changes for a few weeks each spring and autumn, and abbreviations such as CST mean different zones in different countries. The guide to scheduling across time zones shows how to find the overlap — London and New York share four working hours, Beijing and New York none — why a weekly call moves in late October, and how to write deadlines that every reader converts to the same moment. It also explains counting days to a deadline and why business-day counts need a look at the holiday calendar.
Counting days the same way every time
Date arithmetic causes arguments when two people count differently. The date calculator counts the days between two dates, so Monday to Tuesday is one day; business days skip only Saturdays and Sundays; and adding a month to 31 January gives the last day of February. Stating those rules alongside a deadline avoids most disputes about it.