Date & Time Tools
Tools for working with dates and times — calculate ages and durations, count down to events, convert time zones, or time yourself with a stopwatch.
Find an exact age in years, months and days from any birth date, with the leap-year and month-length cases that make the arithmetic less obvious than it looks.
Date Difference CalculatorCount the days, weeks and months between two dates, with both inclusive and exclusive counts and the total in each unit.
Business Days CalculatorCount working days between two dates, skipping weekends and optional US holidays, with the counting conventions that produce different answers.
Date Add / Subtract CalculatorAdd or subtract years, months, weeks and days from any date, with the month-end behaviour that makes date arithmetic non-reversible.
Sleep CalculatorFind the best bedtimes or wake-up times based on sleep cycles, with a clear account of how much the 90-minute figure can actually be relied on.
Timesheet CalculatorAdd up hours worked from clock-in and clock-out times, with breaks and optional pay, handling overnight shifts and the rounding rules employers use.
Due Date CalculatorEstimate a pregnancy due date and current gestational age from the last menstrual period, with an honest account of how few babies arrive on the date.
Time Zone ConverterConvert a date and time between time zones with automatic daylight-saving handling, including the dates when the rules change and disagree.
Online StopwatchAn accurate online stopwatch with lap times, running from the system clock rather than a tick count so it stays correct in a background tab.
Countdown to DateCount down the days, hours, minutes and seconds until any date and time, with a shareable link and correct handling of time zones and clock changes.
Online TimerA full-screen countdown timer with quick presets and an alarm, running in your browser with no account and no installation.
World ClockSee the current time in cities around the world side by side and live, with each city's offset and whether daylight saving is currently in effect.
Meeting Time Zone PlannerFind meeting times that work across multiple time zones at a glance, with working hours shaded so unreasonable slots are obvious before you propose them.
Holiday & Event Countdown HubDays until every major holiday, with moveable feasts computed rather than hard-coded, so the dates stay correct indefinitely.
About these date & time tools
Adding a month is not a well-defined operation, and every date library has had to pick an answer. One month after 31 January is either 28 February, 2 March, or an error, depending on which library you are using — none of them is wrong, because the question does not have an answer. Months have between 28 and 31 days, so month arithmetic is not arithmetic; it is a convention. The same applies to a year, which is why an age calculation that counts days and divides by 365 drifts by a day for roughly every four years of the person’s life. The second thing worth knowing is that not every day has 24 hours. In most of the world with daylight saving, one day a year has 23 and another has 25, and a couple of hundred thousand people live somewhere that has changed its offset entirely — Samoa skipped 30 December 2011 altogether when it moved across the date line, so for that country the date simply does not exist. Any calculation that adds 86,400 seconds and calls the result tomorrow will occasionally land at the wrong hour. The third is that a UTC offset is not a time zone. Storing minus five hours tells you nothing about whether that place observes daylight saving, when it switches, or whether the rule changed last year — and rules do change, several times a year somewhere in the world, which is why time zone databases ship updates. India runs at UTC+5:30 and Nepal at +5:45, so even the assumption that offsets are whole hours is wrong for well over a billion people.