Everyday Math

Date Difference Calculator

Calculate the exact difference between two dates in years, months, days, hours, and minutes. Add or subtract days from a date.

Add / Subtract Days from a Date

How Date Difference Calculations Work

Calculating the exact difference between two dates requires accounting for months of varying lengths and leap years. This calculator uses precise calendar arithmetic — not a simple 365-days-per-year approximation.

The calculation first counts complete years between dates, then remaining months, then remaining days. For example, from January 15, 2020 to March 20, 2025 is exactly 5 years, 2 months, and 5 days (not just a division of days by 365.25).

Common Uses for a Date Calculator

  • Project deadlines: How many working days until a project is due?
  • Legal and financial: Calculating contract periods, notice periods, and maturity dates
  • Age verification: Checking whether someone has reached a required age on a specific date
  • Event planning: How many days until a wedding, birthday, or holiday?
  • Medical: Calculating due dates, treatment lengths, or follow-up schedules
  • Historical research: How long ago did a historical event occur?

Working Days vs Calendar Days

This calculator counts calendar days (including weekends and public holidays). If you need business/working days for project planning, note that calendar days ÷ 7 × 5 gives a rough estimate of working days.

Date Arithmetic Tips

  • To find a date 90 days from today, use the "Add/Subtract" section
  • Lease agreements often use calendar months, not 30-day periods
  • Legal notice periods are usually in calendar days unless specified otherwise
  • Loan maturity dates are in calendar months from the origination date

Frequently Asked Questions

How many days are between two dates?
Enter your start and end dates in the calculator above. It will count the exact number of calendar days, accounting for months with different numbers of days and leap years.
How do I add 30 days to today's date?
Use the "Add/Subtract Days" section below the main calculator. Enter today's date as the base date and type 30 in the days field. The result date will appear immediately.
How many weeks between two dates?
The calculator shows total weeks as part of the results. Total days ÷ 7 (rounded down) gives complete weeks. For example, 90 days = 12 weeks and 6 days.
Does the calculator handle leap years?
Yes. The calculator uses precise calendar arithmetic that correctly handles February 29 in leap years, months with 28, 29, 30, and 31 days, and all other calendar edge cases.
What is the difference between calendar days and business days?
Calendar days count every day including weekends and holidays. Business days (or working days) count only Monday–Friday, excluding public holidays. This calculator counts calendar days. For business days, divide calendar days by 7 and multiply by 5 as an approximation.