📆 Date Calculator
Counting days by hand across month boundaries is error-prone — February alone ruins most mental math. The first tool below counts the exact days between any two dates; the second jumps forward or backward from a date by any number of days.
Handy for deadlines, pregnancy tracking, project plans, visa stays and “90 days from today” questions.
How to use this calculator
This page holds two tools: one counts the days between two dates and another adds or subtracts days from a date. Pick the card you need, then fill in its fields.
- Choose the card that matches your task: Days between two dates or Add or subtract days.
- For days between, set the Start date and End date fields.
- For adding or subtracting, set the Start date, the number of Days, and the Operation (Add or Subtract).
- Read the result date, the weekday it falls on, or the day count from the card.
Frequently asked questions
What does the Date Calculator compute?
The first card counts the exact number of days between a Start date and an End date, also shown as weeks. The second card takes a Start date and moves it forward or backward by a number of Days, depending on the Operation you pick, and shows the resulting date and its weekday.
What formula does the days-between card use?
Both dates are converted to calendar days and the absolute difference is taken, so the count reflects real calendar months including February and leap years. No averaging or 30-day-month assumptions are involved.
Can you give a worked example?
Enter Start date 1 January 2026 and End date 29 September 2026 and you get 271 days between them, shown as 38 weeks + 5 days. Add 30 days to 29 September 2026 and the result is 29 October 2026, a Thursday.
Are there any limits to the dates I can use?
The add/subtract card accepts up to 36,500 days, roughly 100 years, in either direction. The calculation is exact day arithmetic, but it does not account for time zones or time-of-day, only whole calendar days.