Date Difference Calculator
Free date difference calculator. Find the exact days, weeks, months, and years between any two dates. Includes business-day-only and weekend-included options.
Quick answer
Days between two dates = end date Julian day number − start date Julian day number. The calculator handles leap years automatically. For business-days-only counts, subtract weekends and any specified holidays from the total.
Date Difference Calculator
How it works
Calculates the number of days, weeks, months, and years between two dates. Uses calendar math, so it correctly handles leap years and different month lengths.
When to use it
Use this for project planning, contract durations, pregnancy tracking, anniversary countdowns, vacation planning, sentencing/release-date calculations, or anything where you need precise day counts between two dates.
Common mistakes
Confusing inclusive vs exclusive day counts. A contract from Jan 1 to Jan 31 is 30 days exclusive (Jan 1 doesn't count) or 31 days inclusive (both endpoints count). Different contexts use different conventions; check what your situation requires.
How the date difference calculator works
Behind the scenes, this converts both dates to a Julian day number (a continuous count of days starting from a fixed reference point in 4713 BC) and subtracts. This sidesteps every messy date arithmetic case — leap years, end-of-month, daylight saving — because the conversion handles all of them correctly. The result is presented in days, weeks, months, and years. The 'months' figure rounds to the calendar approximation since months have variable lengths; the days figure is exact.
When to use it
Counting days until a vacation, deadline, anniversary, or due date. Computing exact tenure ('How long have I worked here?'). Calculating ages in days for medical applications. Counting business days for project timelines, contract terms, or PTO accrual. Converting between weekly, monthly, and annual subscription anniversaries.
Common mistakes
- Off-by-one errors at boundaries. Is the first day of the range counted? The calculator counts the start day as day 0 and the end day as the count. If you want both endpoints inclusive, add 1.
- Confusing 'months' with '30 days.' A month between Jan 15 and Feb 15 is 31 days. Between Feb 15 and Mar 15, it's 28 (or 29 in leap years). The 'months' figure here is calendar-month based.
- Ignoring time zones for cross-time-zone calculations. A flight that departs Tokyo Friday at 11pm and lands LAX Friday at 4pm is the same calendar day in both cities but very different dates from each side's perspective.
Frequently asked questions
How many days between two dates?
Enter both dates in the calculator above and it shows the exact number of days, weeks, months, and years between them. The math handles leap years and end-of-month boundaries automatically.
How do you count business days only?
Total days minus the number of weekends in that range, minus any specified holidays. For a typical year, business days are about 252 (260 weekdays minus 8-10 holidays). The calculator's business-day option handles this automatically.
Is the start date or end date inclusive?
The calculator counts the difference between the two dates — the start date is day 0, the end date is the count. If you want both endpoints inclusive (e.g. 'how many days am I attending the conference if I arrive Mon and leave Fri'), add 1.