Date Calculator
Adjust the inputs below. Results update as you type.
How it works
Date math answers operational questions: how many days between two dates, what date falls N days from now, or when a deadline lands if only business days count. Calendar rules—month lengths, leap years, and inclusive vs exclusive counting—cause most manual mistakes.
Use difference mode to measure spans for projects, travel, or age-like intervals. Use add/subtract mode to project deadlines. Inclusive counting includes both endpoints; exclusive counting usually measures the gap between them—pick the convention your contract or school policy uses. Business-day mode skips weekends; holidays are jurisdiction-specific and may need manual adjustment.
Time zones and “end of day” definitions are outside pure calendar-day math. For legal, payroll, or shipping SLAs, confirm the governing calendar and holiday schedule rather than relying on a generic weekend skip. Leap days affect February spans and anniversary-style calculations across year boundaries.
Input guidance
- Confirm whether your policy counts days inclusively or exclusively.
- Use business-day mode only when weekends should be skipped.
- Remember holidays are not universal—adjust manually when required.
The formula
Add or subtract days, weeks, months, or years from a start date, or find the span between two dates by counting the days between them.
Worked example
90 days after January 1 is April 1. The span from January 1 to December 31 is 364 days (365 in a leap year).
More examples to test
- Add 10 business days to a Monday start and compare with 10 calendar days.
- Difference from Jan 1 to Dec 31 in a leap year vs a common year.
How to interpret results
Match the counting convention to your contract or school rule. Business-day results still need a holiday calendar for formal SLAs.
When this can be inaccurate
Time zones, exact timestamps, and local holiday calendars are outside pure Gregorian day arithmetic.
Change history
- July 2026: Business-day and inclusive/exclusive counting guidance expanded.
- June 2026: Gregorian add/diff paths reviewed.
Site-wide corrections also appear on the corrections log.
Find productivity tools for everyday workflows
General recommendation, not professional advice.
Frequently asked questions
How do I add days to a date?+
Count forward from the start date, rolling over month and year boundaries. The calculator handles varying month lengths and leap years automatically.
Does it count both end dates?+
Typically the difference excludes the start and includes the end (or vice versa). Check whether you want inclusive or exclusive counting for your purpose.
Can it skip weekends?+
Business-day calculations exclude weekends (and sometimes holidays), useful for deadlines and shipping estimates.
Why are outputs slightly different from another tool?+
Different tools can use different rounding rules, default assumptions, and treatment of edge cases.
How can I improve estimate reliability?+
Use verified inputs from real records and re-run calculations after major assumption changes.