Date calculators · Ages & date spans
Date Duration Calculator
Turn a span of dates into years, months and days, with the calculation steps in plain sight.
Your calculation
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Choose your dates.
Select your counting rules and calculate.
Calculation details
| Step | Value |
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How to use this calculator
Enter two dates and calculate. The result separates complete calendar months from the remaining days, shows the date reached by those months, and compares the span in total days and whole weeks.
This is an anchored calendar-month calculation, not days divided by 30 or 365. The earlier date supplies the day of month; a shorter target month clamps to its last day. Reversing the two dates keeps the same magnitude and marks the direction as backward. No extra endpoint date is added.
A worked example
January 31 to March 30, 2026 is one month and 30 days: one anchored month reaches February 28, then 30 more days reach March 30. The total is 58 calendar days.
Why can different calculators show different month totals?
Months have different lengths, and tools may use borrowing, average-month lengths or month-end conventions. This tool exposes its month anchor so the answer is reproducible. Use the general calculator when you need inclusive calendar-day counting instead.
Which calendar and years are supported?
These tools use Gregorian calendar dates for years 1–9999, without historical calendar-switch dates. They count dates, not elapsed hours. Today buttons use the current date in your browser's time zone.
What happens to my dates?
Calculations run on your device. Saving a calculation is optional and keeps it in this browser. A setup link contains the dates and settings you entered; anyone with the link can read them. Use one tab per saved calculator. Clear saved data from Privacy & settings.