How do I find the number of days between two dates?
Choose “Days between two dates”, enter the start and end dates, then calculate. The tool returns the signed day difference and absolute totals.
Date Calculator
Compare two calendar dates or project a new date by adding or subtracting days, weeks, months, or years.
Calculate with dates
Choose difference or add/subtract mode, then enter the dates and amounts you need.
About this calculator
How to use Date Calculator, plus the formulas and logic behind the results.
Tool description
The Date Calculator finds how many days separate two dates, or builds a new date by adding or subtracting a chosen amount of days, weeks, months, or years. It helps with planning deadlines, travel, and personal milestones.
How to use
- Select difference, add, or subtract.
- Enter the start/base date (and end date for difference mode).
- For add/subtract, enter the amount and unit.
- Select Calculate to view the result.
Formulas & reference
difference days = end_date − start_date (calendar days)result_date = base_date ± amount of unitweeks = days × 7 when converting for display
What this tool covers
- Exact day count between two calendar dates
- Add or subtract days, weeks, months, or years
- Useful for deadlines, project plans, and anniversaries
Calculation logic
Difference mode uses PHP DateTimeImmutable day arithmetic and reports signed day counts plus absolute weeks/days. Add/subtract modes apply calendar-aware modifiers (+N days/weeks/months/years) so month lengths and leap years are handled correctly.
Month and year shifts follow calendar rules (for example, Jan 31 + 1 month → Feb 28/29). Results use the server calendar, not a specific business holiday calendar.
Date Calculator FAQ
Common questions about this calculator and how to use the results.
Can I add months or years to a date?
Yes. Switch to Add mode, enter the base date, amount, and choose months or years as the unit.
What happens if I add one month to January 31?
The result follows calendar rules and lands on the last valid day of February (28 or 29 in a leap year).
Does this exclude weekends?
No. Use the Business Days Calculator when you need weekday-only counts.
Is the end date included in the day count?
Difference mode counts full calendar days between the two dates (end − start). Same-day inputs return 0 days.
Can I calculate a past date?
Yes. Use Subtract mode, or enter an end date earlier than the start date in difference mode to see a negative day count.
Are leap years handled?
Yes. Day and month arithmetic respects leap-year February 29 when it applies.
What timezone does the date calculator use?
Dates are treated as calendar dates without a clock time, so timezone offsets do not change the result.