Time and date tools
Timers and clocks that keep running offline, and date arithmetic that follows calendar rules — leap years, month lengths and daylight saving included.
Free · run in your browser · nothing uploaded
Timers
Music practice
Keep a steady tempo and tune up before you play.
Sounds and ambience
Everything here is generated in the browser, so it keeps working offline.
Sky and space
Date and time arithmetic
About these tools
Date arithmetic is deceptively awkward: months vary in length, leap years break naive formulas, and time zones shift the answer depending on where the question is asked from. The tools here follow calendar rules rather than approximations, which is why their results match what forms and institutions expect.
Alongside the calculators sit the practical ones — timers, countdowns, a pomodoro clock. Those run entirely on your device, so they keep counting whether or not the connection does.
Questions people ask
Does the time zone converter handle daylight saving time?
Yes. It uses the IANA time zone database built into your browser, so a conversion is correct for the specific date you pick — a 15:00 New York meeting lands at a different London time in March, when the US has changed its clocks and the UK has not yet, than in July.
Which week-numbering system does Week number use?
ISO 8601, the one used across Europe and in most business software: weeks start on Monday, and week 1 is the week containing the year's first Thursday. That is why 1 January can fall in week 52 or 53 of the previous year.