How the date calculator works
Pick a start date and an end date, and the calculator tells you the gap in several forms: calendar years, months and days; total months; total weeks; and total days. Leave the second date as today’s date to find an exact age. If you enter the dates in the wrong order the tool swaps them for you and tells you it did.
The result in years, months and days is calculated the way people naturally count. It first counts whole months forward from the start date, and then counts the remaining days. This avoids a common mistake of treating every month as 30 days. When the start day does not exist in a month, such as the 31st in April, the count uses the last day of that month. Total days are taken directly from the calendar, so leap years are always handled correctly.
When the first date is a birth date, the note under the result also shows how many days remain until the next birthday. Birthdays on 29 February are counted on 28 February in non-leap years.
All calculation happens in your browser, using calendar dates without a time zone, so the answer does not change depending on where you are or when daylight saving time begins.
How the calculation is done
Months = (year2 − year1) × 12 + (month2 − month1), minus 1 if day2 < day1
Days = end date − (start date + Months)
Years = whole 12-month blocks in Months
Total days are the difference between the two dates divided by the length of a day. Because dates are compared at midnight UTC, there is no daylight-saving distortion.
Worked example
Consider a birth date of 15 June 1990 and an end date of 21 October 2026. From June 1990 to October 2026 is 36 years and 4 months, and since the 21st comes after the 15th, no month has to be removed. The remaining days are 6, so the answer is 36 years, 4 months, 6 days. That is 13,277 days in total, or 1,896 full weeks.
Everyday uses
- Age checks for forms, school cut-off dates and eligibility.
- Project planning: count the days between a start date and a deadline.
- Anniversaries and milestones such as years of service or time since an event.
- Pregnancy and baby tracking: weeks since a starting date.
- Contracts and notice periods where the number of days matters. Always confirm legal deadlines against the exact wording of the agreement.
Frequently asked questions
Does the calculator include the end date?
The count is the elapsed time from the first date to the second, so the end date itself is not counted as an extra day. From 1 January to 2 January is 1 day. If you need to count both days inclusively, add one.
How are leap years handled?
Total days come straight from the calendar, so 29 February is always counted when it falls inside the range. For years, months and days, months are counted on the calendar, which also respects different month lengths.
Why might another tool give a different number of months and days?
Different tools use different conventions when the start day does not exist in a month. This calculator clamps to the last day of the month. The total number of days is unambiguous and will match.
Can I calculate a date in the future?
Yes. Enter any later date as the end date to see how long remains. This is useful for countdowns to events, deadlines or due dates.
Is my birth date stored anywhere?
No. The calculation runs entirely in your browser. If you use the shareable link, the dates are placed in the page address only, so anyone you send the link to can see them.