Date Difference Calculator
Days, weeks, months and years between two dates — plus add or subtract time from a date.
Find days between two dates, or add and subtract days, weeks, months and years from any date. Get results in days, weeks, months and years, with correct month-length and leap-year handling.
Calendar: Gregorian, leap-year aware, month arithmetic clamped to valid days.
Difference between two dates
Add or subtract from a date
How to use the Date Difference Calculator
- Pick the two dates.
- Read the difference in days, weeks, months and years.
- Use the arithmetic mode to add or subtract time from a date.
Frequently asked questions
How do I count days between two dates?
Select both dates above and the tool shows total days instantly, including the breakdown in months and years.
Does it include the end date?
It counts the full 24-hour spans between the dates; for an inclusive count, add one day.
How does it handle leap years?
Leap days are counted correctly — February 29 is included in any range that covers it.
Can I add months to a date?
Yes — month arithmetic clamps to valid days (for example Jan 31 + 1 month = Feb 28 or 29).
Fun facts about Date Difference Calculator
- The Gregorian calendar (used today) was introduced by Pope Gregory XIII in 1582 to correct the drift of the Julian calendar — 10 days were skipped when it was adopted.
- A year is actually 365.2422 days, not exactly 365 — which is why we have leap years. But even leap years aren't perfect, so century years divisible by 400 are also leap years.
- February's short length dates back to the early Roman calendar; the popular story that Augustus took a day from February for August is a medieval myth.
- The ISO 8601 date format (YYYY-MM-DD) is the international standard — it sorts correctly as text and avoids ambiguity between US (MM/DD) and European (DD/MM) formats.
- There is no year 0 in the Gregorian calendar — it goes from 1 BC directly to 1 AD, which is why centuries and millennia start in years ending in 01.