Date and time calculators

Calendar arithmetic is deceptively hard: months change length, leap years move the goalposts and weekends do not count. Each of these explains the method rather than just returning a number.

• Days Between Dates Count the exact days between two dates, in calendar or business days, with the breakdown in years, months and days
• Perpetual Calendar The calendar of any month of any year, with the weekdays, the leap year check and the ISO week numbers
• Age Calculator Your exact age in years, months and days, counted the way it is actually counted: stepping month by month from your date of birth, not dividing days by 365
• Add Days to a Date Add or subtract days from any date and get the result with its day of the week, plus what the answer would be if you counted only working days
• Business Days Calculator Count the working days between two dates, weekends excluded and with your own holidays deducted
• Days Until Calculator How many days are left until a date, broken down into years, months and days, with the working-day count and the day of the week it lands on
• Weeks Between Dates The number of whole weeks between two dates, the days left over, and the same period expressed as a decimal
• Months Between Dates The number of whole months between two dates, counted by stepping month by month rather than dividing days by 30
• Week Number Calculator The ISO week number for any date, plus the day of the year and the quarter
• Day of the Week Calculator What day of the week any date fell on, or will fall on
• Leap Year Calculator Whether a year is a leap year, and why
• Hours Calculator Add up or subtract a list of durations written as 8:30, 7.5 or 90 minutes, and get the total in hours and minutes as well as in decimal hours
• Years Between Dates From 12 October 1492 to 12 October 2026 there are exactly 534 years
• How Many Days Have I Lived Ten thousand days is twenty-seven years and four months: a milestone nobody celebrates because nobody works it out
• Hours to Minutes Converter Two hours and forty-five minutes is 165 minutes and 9,900 seconds
• Decimal Hours Converter Seven hours and forty-five minutes is 7.75 decimal hours, and 7.45 means nothing of the sort
• Time Zone Difference London and New York are five hours apart most of the year and four for two weeks in March, because the clocks change on different weekends
• Time Zone Converter A meeting at 23:30 in Madrid lands at 6:30 the next morning in Tokyo
• Deadline Calculator An invoice on 30-day terms issued on 15 March falls due on 14 April in calendar days, and on the 27th if the contract says business days
• Anniversary Calculator The silver anniversary is at 25 years and the golden one at 50, and that count is always further off than it feels
• Time Duration Calculator A concert from 20:30 to 02:15 lasts five and three quarter hours, not minus eighteen
• Retirement Countdown Born in 1990 and retiring at 65, you have about 10,500 working days left
• Date of Birth From Age Someone who is 30 today was born on one of 365 possible days, not on a single date
• Excel Date Serial Number 7 September 2026 is number 46,272 to a spreadsheet