Quirkulator

Date Calculators

18 calculators covering adding, subtracting and comparing dates, each with its formula and worked examples.

Date Calculators brings together 18 calculators for adding, subtracting and comparing dates, including Add Days to Date, Date Difference Calculator, Days Between Dates Calculator and Half Birthday Calculator.

Every page states its method up front — which formula, which convention, which assumptions — because those choices change the answer, and a calculator that hides them is only pretending to be precise.

All 18 pages compute in your browser: nothing you type is sent anywhere, and results update as you edit. Each one carries worked examples, interpretation bands where a score needs context, and a FAQ answering what people actually ask about that calculation.

The collection is part of Date & Time, and every page links to the neighbouring calculations you usually need next.

18 pages in this collection

Add Days to DateAdd any number of days to a date and get the exact result, weekday included.Add Months to DateAdd or subtract calendar months with correct end-of-month clamping.Age CalculatorWork out an exact age in years, months and days, plus the totals in days, weeks and hours.Date Difference CalculatorBreak the gap between two dates into years, months and days, with every total alongside.Date Plus Business DaysAdd working days to a date, skipping every Saturday and Sunday along the way.Day of the Week CalculatorFind which weekday any date falls on, past or future, with its calendar position.Day of the Year CalculatorConvert a date into its ordinal day number, and see how much of the year has elapsed.Days Between Dates CalculatorCount the days between two dates, inclusive or exclusive, split into weekdays and weekend days.Days Since a Date CalculatorMeasure how long ago something happened, in days, weeks, months and working days.Days Until a Date CalculatorCount down to a future date in days, weeks and working days from today.Half Birthday CalculatorFind the date exactly six calendar months from a birthday, and when it next comes round.ISO Week Number CalculatorFind the ISO 8601 week number for any date, with the Monday and Sunday that bound it.Leap Year CheckerTest any year against the full 4/100/400 rule and see the next leap years in sequence.Months Between Dates CalculatorCount whole calendar months between two dates, with the leftover days and a decimal equivalent.Next Birthday CountdownCount the days to the next birthday, the age being reached and the weekday it falls on.Subtract Days from DateCount backwards from a date to find the day a deadline or notice period started.Weeks Between Dates CalculatorConvert a date range into whole weeks and leftover days, with fortnights and ISO week numbers.Years Between Dates CalculatorCount complete years between two dates by anniversary, with the decimal equivalent alongside.

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