Date Calculator
Calculate D-day, date differences, and add/subtract days.
D-Day Calculator
Date Difference
Add/Subtract Days
About this tool
A three-in-one date utility: count down to a future event (D-day), measure the gap between any two dates in days/weeks/months/years, or add and subtract days from a starting date. All calculations run instantly in your browser using local time. Useful for project deadlines, event planning, contract terms, and personal milestones.
How to use
- For D-day countdown, set your target date and read D-N or D+N.
- For date difference, enter both start and end dates to see the spans.
- For add/subtract, choose a base date and type a positive or negative number of days.
- Use the formatted date with weekday for quick verification.
- Bookmark the page with your dates pre-filled in the URL.
Common use cases
- Counting down to exam day, project deadline, or wedding.
- Computing the number of nights for a hotel stay or rental.
- Calculating contract duration or notice periods.
- Estimating delivery dates by adding shipping days.
- Planning a sprint, vacation, or marathon training schedule.
Frequently asked questions
Q. How are months and years calculated?
A. Months are approximated as 30 days and years as 365 days for quick estimation. For exact calendar months, use the age calculator.
Q. Why does today show as D-1 in some time zones?
A. The countdown uses your device's local midnight. Crossing midnight or different time zones can shift the count.
Q. Can I add a negative number of days?
A. Yes. Negative numbers subtract days from the base date.
Q. Are weekends excluded?
A. No, all days are counted. Use a business-day calculator if you need to exclude weekends.