Date Calculators

Choosing the right date calculator

Most date questions fall into one of three shapes, and picking the matching tool saves a lot of confusion.

Comparing two dates you already have

Use the date difference calculator when you want the answer in years, months and days, and the days between dates calculator when you want a plain day count with a weekday breakdown. The two agree on the totals; they differ in what they emphasise.

Finding a date you do not have yet

Use add or subtract days from a date. It handles the awkward cases properly: adding a month to 31 January gives 28 February rather than an invalid date, and adding a year to 29 February clamps to the 28th in non-leap years.

Understanding a date you are looking at

The week number calculator gives the ISO week, the day of the year, the quarter and the weekday, and works in reverse to tell you which dates a given week covers.

The two things that trip people up

Whether the endpoints count

Monday to Friday is four days of elapsed time and five days of working week. Neither is wrong — they answer different questions. Every calculator here states which reading it used, and lets you change it.

Month ends

Months are not a fixed length, so “one month later” has to be defined. The convention used throughout this site, and by ISO 8601 and most software, is to keep the same day number and clamp to the end of the month when that day does not exist. One consequence is that the arithmetic is not reversible: 31 January plus one month is 28 February, but 28 February minus one month is 28 January.

If you need weekends and holidays excluded

These calculators count every calendar day. To exclude weekends and public holidays, use the business day calculators, which apply the holiday calendar for your country and let you set which days count as your weekend.