Date After N Days Calculator
Add or subtract any number of days from a date to find the exact calendar date and weekday it lands on.
How it works
result = start ± N days · weeks = N ÷ 7 · calendar span = years-months-days between the two dates
Days are added straight onto the date object, so month boundaries, leap days and year rollovers are all handled by the calendar itself — no manual carrying. The result also comes back as a number of weeks and as a years-months-days span, which is handy when a deadline is quoted as "within 90 days" but you think in months. Pick "before" to walk backwards from the start date.
Worked example
100 days after 15 Sep 2026 is 24 Dec 2026, a Thursday — that is 14.3 weeks, or 3 months and 9 days on the calendar.
Frequently asked questions
Does it count the start day?
No — day 1 is the day after the start date. "100 days after" the 15th lands on a date 100 days later, not counting the 15th itself.
Can I go backwards in time?
Yes — choose "Before" to subtract the days and find an earlier date, for example a deadline that is a set number of days before an event.
Are weekends and holidays skipped?
No — this counts every calendar day. To skip weekends, use a business-days calculator instead.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.