Days Between Dates
Count days, weeks, months and business days between two dates.
Days between
0
0 business days (Mon–Fri)
Weeks
0
Months
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Years
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Business days
0
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How the Days Between Dates works
The Days Between Dates calculator counts the exact number of days, weeks, months, and business days separating any two calendar dates — making it essential for project managers, legal professionals, students, and anyone tracking deadlines, contracts, or personal milestones.
At its core, the calculator converts each date into an absolute day count (often measured from a fixed epoch, such as January 1, 4713 BC in the Julian Day system, or simply a modern reference point) and subtracts the earlier value from the later one. This subtraction yields the raw date difference in days, which is then divided by 7 to express the duration in weeks, and further approximated into months by accounting for each calendar month's variable length. Because months range from 28 to 31 days, the 'months between' figure is always an approximation unless you specify full calendar months.
Business days — also called working days — are calculated by removing Saturdays and Sundays from the raw day count, and optionally subtracting public holidays. In the United States, the standard assumption is a Monday-through-Friday workweek, but many countries observe different weekend structures (for example, Friday–Saturday weekends in several Middle Eastern nations). When you need a precise business-day count for a contract or legal deadline, always confirm which holiday schedule applies, because omitting even one public holiday can shift a due date by a full day.
A common mistake users make is confusing inclusive and exclusive counting. If you want to know how many days fall between March 1 and March 5, the exclusive count is 4 days (the gap), while the inclusive count is 5 days (counting both endpoints). Legal documents, shipping carriers, and financial instruments often specify which convention they use — 'within 30 days' versus 'on or before the 30th day' — so matching the right counting method to your context is critical for avoiding errors.
The calculator also handles edge cases that trip up manual calculations: leap years (February 29 adds one day to any span crossing it), daylight saving time transitions (which can make certain days 23 or 25 hours long, though date-only calculators ignore clock time), and year-end rollovers. For multi-year durations, these factors accumulate, so relying on a precise tool rather than rough mental arithmetic is especially important for anything with financial, legal, or health consequences.
Formula
Days = (later date − earlier date) ÷ 86,400,000 ms
Pro tips
- Great for deadlines, leases and project timelines.
Key terms
- Date Difference
- — The total number of calendar days that separate two dates, calculated by subtracting the start date from the end date in absolute day units.
- Business Days
- — Weekdays (Monday through Friday in most regions) excluding official public holidays, used to measure working time rather than calendar time.
- Inclusive vs. Exclusive Counting
- — Inclusive counting includes both the start and end dates in the total, while exclusive counting counts only the days strictly between them — a distinction that matters in legal and financial contexts.
- Leap Year
- — A calendar year containing 366 days (with February 29 added) that occurs every 4 years, with exceptions for century years not divisible by 400, affecting any date range that crosses February of that year.
- Duration
- — The measured length of time between a start and end point, expressible in days, weeks, months, or business days depending on the use case.
- Epoch Date
- — A fixed reference date from which absolute day counts are calculated, allowing any two calendar dates to be compared by simple subtraction.
