Three date calculations in one place
- D-day: how many days until (or since) a target date — for exams, anniversaries, deadlines.
- Days between: the number of days between two dates — for trip lengths or day counts.
- Add / subtract days: the date N days after (or before) a base date — for due dates.
Which way the D-day counts
A future target shows D-number (days left), a past one shows D+number (days since), and the day itself shows D-Day. The result also includes the weekday of that date, so you instantly know if it lands on a weekend.
Things people get wrong
- Counting the start day: "100 days from today" differs by one depending on whether today is day 0 or day 1. That's why the difference mode shows both the plain difference and the including-both-ends count.
- Leap years: any range crossing February 29 is handled automatically — easy to miss when adding 30/31 by hand.
- Off-by-one anniversaries: many "100-day" counts treat the first day as day 1, so the tool's "99 days later" is often the popular 100th day.
Everything is computed in your browser. For your age, see the Age Calculator; for other units, the Unit Converter.