Day Counter
Count the number of days between two calendar dates. Works forward or backward; useful for deadlines, project timelines, and age-in-days.
Last updated: October 2026
Days Between
364 days
Formula below · 2 sources (iso.org, developer.mozilla.org) · Updated Oct 2026
Compare with similar
About this calculator
The day count between two dates is the elapsed number of full 24-hour periods. This calculator parses the two dates in ISO 8601 form (YYYY-MM-DD), computes the millisecond difference, and divides by 86 400 000 (the number of milliseconds in a day).
It rounds to the nearest whole day, so daylight-saving-time shifts (which subtract or add an hour, well under a full day) do not offset the result. If you need hour-level precision across a DST boundary, work in UTC or use a full datetime pair.
Backward differences (end date earlier than start) return a negative number, which is often what you want for questions like 'how many days ago was…'. If you always want a positive count, take the absolute value.
How to use
Example: days in 2026. Start = 2026-01-01, End = 2026-12-31. Result = 364 days between the dates; choose 'include the end date' to get 365, the number of calendar days in the year. Example: countdown to a deadline. Start = 2026-09-18, End = 2026-12-25. Result = 98 days (12 left in September, 31 in October, 30 in November and 25 in December), which is exactly 14 weeks. If the end date is earlier than the start date, the result is negative.
Frequently asked questions
Are the start and end dates included in the count?
By default the result is the difference between the dates, so 2026-03-02 to 2026-03-06 (Monday to Friday) is 4 days. Choose 'include the end date' to count both endpoints, which gives 5. Use that option for questions like 'how many days is the trip' or 'how many days of the year'.
How does daylight saving time affect the count?
DST shifts the clock by an hour twice a year, but this calculator rounds to whole days, so DST cannot change the answer. The underlying arithmetic uses UTC millisecond timestamps; the rounding step absorbs the ±1 hour DST offset.
Can I use it for age in days?
Yes. Enter the date of birth as the start date and today's date as the end date; the result is age in days. The years tile divides by 365.2425, the average length of a Gregorian year.
What date format does it accept?
ISO 8601 (YYYY-MM-DD) is the safest — it is unambiguous across locales. Formats like '3/4/2026' are parsed by the JavaScript Date constructor, but the interpretation differs by locale (US: March 4, UK: April 3). Stick with YYYY-MM-DD to avoid off-by-a-month bugs.
Related calculators
Sources & references
Think a result is wrong? Report a problem with this calculator.