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Date Calculator — Add or Subtract Days From Any Date

By Sofia Andersen · Last updated 15 October 2026

Deadlines have a habit of landing on Saturdays. Type in a start date and a number of days and this page tells you where you land, weekday included. Handy for deadlines, due dates, return dates, and “90 days from now” questions.

Enter your numbers

Result

Adding weeks is the easy case

Adding days moves forward on the calendar; subtracting moves backward. The calendar does the uneven work: months have 28–31 days, and leap years add a 29 February every four years (with century exceptions). You never need to adjust for any of that by hand. The calculator counts real calendar days.

Result date = Start date + Days (or minus Days). Weekday shifts by Days mod 7. Adding whole weeks is the one case where the weekday never changes: 6 weeks from a Thursday is always a Thursday. Adding days shifts the weekday by the remainder after dividing by 7. Days are the most reliable unit, exact calendar days. Weeks are 7 days each. Months are calendar months, and the day may shift if the month is shorter (e.g. 31 Jan + 1 month).

Four jumps from one Thursday

Starting from Thursday, 15 October 2026:

  • Add 45 days: 15 October + 45 days = Sunday, 29 November 2026. (16 days left in October take you to 31 October, then 29 more days into November.)
  • Subtract 30 days: 15 October − 30 days = Tuesday, 15 September 2026. (15 days back to 30 September, then 15 more into September.)
  • Add 90 days: 15 October + 90 days = Wednesday, 13 January 2027.
  • A second check: 25 December 2026 − 100 days = Wednesday, 16 September 2026.

Notice how the weekdays move: +45 days shifts the weekday by 45 mod 7 = 3 days (Thursday to Sunday), and −30 days shifts it by −30 mod 7 = −2 days (Thursday to Tuesday). The calculator confirms all of this automatically.

Before you trust the landing date

Result date is the date you land on. Weekday tells you whether it falls on a weekend, the detail that matters most for deadlines and bookings. If you added months rather than days, check the result date carefully when the start day is 29, 30, or 31: months are uneven, so “one month after 31 January” has no exact answer and tools handle it differently (most clamp to the last day of the target month). Month arithmetic is approximate by nature, so prefer days or weeks when the exact date matters. This tool counts calendar days, not business days; a result that lands on Saturday or Sunday may need shifting to Friday or Monday for office deadlines. Holidays are not accounted for, so check them separately for legal or delivery deadlines.

The jumps people ask for most are 7, 14, 30, 45, 60, and 90 days from today, plus 6 weeks, 3 months, 6 months, 1 year, and counting back 30, 60, or 100 days.

Questions

What date is 90 days from today?

Enter today as the start date and add 90 days. From 15 October 2026, 90 days later is Wednesday, 13 January 2027.

How do I add weeks instead of days?

Use the weeks mode. Each week is 7 days, and the weekday stays the same. Six weeks from a Thursday is always a Thursday.

Why does adding a month sometimes change the day number?

Because months have different lengths. Adding one month to 31 January cannot land on 31 February, so tools clamp to the last day of February. Use days when the exact date matters.

Can I find what day of the week a date falls on?

Yes. Every result shows its weekday, so you can check whether a deadline, birthday, or event lands on a weekend.

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