Date & Time Calculators
Date and time calculators answer questions that are awkward to do in your head because months vary in length and leap years get in the way. They come up in project planning, visa and contract paperwork, event organising and anything involving colleagues in other countries. The Date Difference Calculator counts the interval between two dates in days, weeks and months, which is what notice periods, residency applications and rental agreements usually ask for. The Age Calculator is the same arithmetic aimed at birthdays, giving an exact age in years, months and days as of today or any date you choose, and it is the quicker option when you just have a date of birth. The Time Zone Converter maps a moment in one place to the local time somewhere else, including the daylight saving shifts that make calls land an hour out twice a year. Use it before you send an invitation rather than after. The Countdown Timer tracks the remaining time to a fixed point such as a launch, an exam or a flight, and keeps running on screen while you work. All four run in the browser with no sign-up, and no dates you enter are stored anywhere.
4 tools available
Showing 1–4 of 4
Date Difference Calculator
Count the exact days, weeks and calendar months between any two dates, leap years included.
Age Calculator
Calculate an exact age in years, months and days from any date of birth, with totals and a next-birthday countdown.
Time Zone Converter
Convert any date and time from one city to several world time zones at once, with business-hours flags.
Countdown Timer
Count down to a target date and time or for a set duration, with a label, progress bar and end alert.
Two ways of measuring the same countdown
Target mode works the opposite way round. It takes the date and time you selected, compares it with your device's current clock, and derives the remaining seconds from the difference. Because the target is a fixed point, the remaining time is recomputed against the clock rather than simply decremented, which keeps a long countdown accurate even if the tab is inactive for a while.
The display then converts the remaining seconds back into days, hours, minutes and seconds for reading. Elapsed time is the total minus the remaining time, and the progress bar shows elapsed divided by total as a percentage. Pausing stops the countdown and holds the remaining value until you resume.
A 45 minute timer partway through
Eighteen minutes in, the elapsed time is 18 multiplied by 60, which is 1080 seconds. The remaining time is 2700 minus 1080, which is 1620 seconds, displayed as 27 minutes and 0 seconds. The progress bar reads 1080 divided by 2700, which is 0.4, so 40 per cent complete.
Now take target mode instead. Suppose today is 21 September and you set a target of 1 October at 09:00, with the current time 14:30 on 21 September. From 14:30 on 21 September to 14:30 on 30 September is 9 days. From there to 09:00 on 1 October is another 18 hours and 30 minutes. The countdown therefore reads 9 days, 18 hours, 30 minutes, which is 9 multiplied by 86400 plus 18 multiplied by 3600 plus 30 multiplied by 60, or 844200 seconds.
Keeping the countdown reliable and reading it correctly
Target mode reads the time from your device's own clock and timezone. A countdown to a deadline expressed in another timezone will be wrong unless you convert the target time yourself first, which catches people out with submission deadlines quoted in UTC or in a different country.
The alert sound needs your device volume up and the browser not muted, and some browsers block audio until you have interacted with the page, which starting the timer satisfies. Finally, the progress bar reflects the proportion of the countdown that has elapsed, not progress through whatever task you are doing, so treat it as a clock rather than a measure of how much work is left.