Date Difference Calculator
Find the exact number of years, months, weeks, and days between any two dates.
What is a date difference calculator?
A date difference calculator finds the exact time between two dates and expresses it two ways: as a calendar span (years, months and days) and as totals (days, weeks, months and hours). Enter any two dates above — the order does not matter — and it counts every day between them, leap days included.
It is the tool behind dozens of everyday questions: how many days until a deadline, how long you have worked somewhere, how many weeks pregnant, how long a warranty has left, how many days a contract has run, or the exact length of a trip. It also removes the guesswork from the two things people get wrong with dates — months of unequal length and whether to count the end day.
Calendar span vs total days
"Years, months, days" and "total days" answer different questions. From January 1, 2020 to September 16, 2026 is 6 years, 8 months, 15 days — the calendar answer — and 2,450 days, or exactly 350 weeks. The calendar span is what you use for ages, tenure and anniversaries; the day count is what you use for deadlines, interest calculations and anything a contract defines "in days".
Months are the awkward unit because they run from 28 to 31 days. The calculator counts a month as the same day number in the next month (January 15 to February 15 is one month), then counts leftover days. That is the convention banks, HR systems and courts use.
Inclusive or exclusive: do you count the end date?
The calculator counts the days between the dates, so Monday to Friday of the same week is 4 days. If you need to count both ends — nights in a hotel are exclusive, but days of a rental, days of leave taken or "days on site" are usually inclusive — add 1. Contracts and statutes normally say which they mean; if one says "within 30 days of", the day of the triggering event is usually excluded and the 30th day counts.
Days in each month
| Month | Days | Month | Days | Month | Days |
|---|---|---|---|---|---|
| January | 31 | May | 31 | September | 30 |
| February | 28 (29 in leap years) | June | 30 | October | 31 |
| March | 31 | July | 31 | November | 30 |
| April | 30 | August | 31 | December | 31 |
Leap years are years divisible by 4, except century years, which must be divisible by 400 — so 2024 and 2028 are leap years, 2100 is not, and 2000 was. A common year has 365 days (52 weeks and 1 day); a leap year has 366.
Common intervals from a date
| From March 15, 2026 | Lands on | Used for |
|---|---|---|
| + 30 days | April 14, 2026 | Invoice terms, return windows |
| + 60 days | May 14, 2026 | Notice periods, trial periods |
| + 90 days | June 13, 2026 | Probation, prescriptions, quarterly reviews |
| + 180 days | September 11, 2026 | Visa and passport validity rules |
| + 6 months | September 15, 2026 | Leases, notice — note it is 184 days, not 180 |
| + 1 year | March 15, 2027 | Warranties, anniversaries |
"Six months" and "180 days" are not the same thing, and neither is "90 days" and "three months". When a document says days, count days; when it says months, use the same calendar day in the later month — and use the date add calculator to go forward or back from a date.
Business days
This calculator counts every calendar day. For working days — Monday to Friday, excluding weekends — use the working days calculator, which can also skip U.S. federal holidays. As a rule of thumb, a full year has 260–262 weekdays (261 in 2026), a month has 20–23, and each week of calendar time is 5 working days.
Formula
Total days = the later date − the earlier date, counted on the calendar (so leap days are included automatically). Then:
- Weeks = days ÷ 7
- Hours = days × 24
Years, months and days are found by subtracting component by component, borrowing when a value goes negative:
- Days = later day − earlier day; if negative, borrow a month and add the number of days in the month before the later date.
- Months = later month − earlier month (minus any borrowed month); if negative, borrow a year and add 12.
- Years = later year − earlier year (minus any borrowed year).
Total months = years × 12 + months. If the first date is after the second, the calculator swaps them and shows the result with a minus sign.
Worked example
January 1, 2020 to September 16, 2026:
- Years: 2026 − 2020 = 6; months: 9 − 1 = 8; days: 16 − 1 = 15 → 6 years, 8 months, 15 days
- Total days: 2,450 (six years of 365 or 366 days plus 259 days into 2026; leap days in 2020 and 2024 included)
- Weeks: 2,450 ÷ 7 = 350 weeks exactly; months: 6 × 12 + 8 = 80; hours: 58,800
A case with borrowing — March 25 to September 16, 2026: days 16 − 25 is negative, so borrow August's 31 days: 16 + 31 − 25 = 22; months 9 − 3 − 1 = 5 → 5 months, 22 days, or 175 total days.
Same-week check: Monday, March 2 to Friday, March 6, 2026 is 4 days between, 5 days inclusive.
How to use this calculator
- Enter the start date.
- Enter the end date (today is the default). If you enter them backwards, the calculator still works and marks the result negative.
- Read the difference as years, months and days, and as total days, weeks, months and hours.
- Add 1 to the day count if your situation counts both the first and last day.
Typical uses
- Deadlines and terms — days left on a return window, a lease, a visa, a warranty or a statute of limitations.
- Tenure and anniversaries — exact length of employment, a relationship, or time since a purchase.
- Interest and pro-rating — daily interest, rent or subscription refunds are all "amount ÷ days in period × days used".
- Health — weeks pregnant, days since surgery, length of a medication course.
- Travel — trip length for insurance, Schengen 90/180-day rule, days abroad for tax residency.
Related tools
- Age calculator — exact age from a date of birth
- Working days calculator — weekdays only, with holidays
- Date add calculator — a date plus or minus days, weeks or months
- Days until calculator — countdown to an event
Frequently asked questions
Does this count leap years?
Yes. Total days are counted on the actual calendar, so every February 29 in the range is included — January 1, 2020 to September 16, 2026 contains two (2020 and 2024) and comes to 2,450 days. Leap years are those divisible by 4, except century years not divisible by 400: 2024 and 2028 are leap years; 2100 is not.
Why are the months and days not a simple subtraction?
Because months have different lengths, subtracting day numbers can go negative — March 25 to September 16 gives 16 − 25 = −9. The calculator borrows a month, adds the length of the previous month (August, 31 days) and reports 5 months 22 days. This is the same convention used for ages, employment tenure and most legal date arithmetic.
Does this include the end date?
No — it counts the days between the two dates, so Monday to Friday is 4 days. Add 1 if both ends should count, as for days of a rental, days of leave, or an inclusive date range in a contract. Hotel nights, interest periods and "days until" countdowns are exclusive, so use the figure as shown.
Can I calculate business days only?
Not here — this tool counts calendar days. The working days calculator on this site counts Monday to Friday and can exclude U.S. federal holidays. For a quick estimate, a calendar month has 20–23 weekdays and a year has 260–262.
How many days are in a year?
365 in a common year and 366 in a leap year, which is why a year is 52 weeks plus one day (or two in a leap year). Over a four-year cycle the average is 365.25, the figure used in "days ÷ 365.25" age estimates. Business years have about 261 weekdays.
Is "90 days" the same as "3 months"?
No. Three months from March 15 is June 15, which is 92 days; 90 days from March 15 is June 13. The difference is small but matters for visas, prescriptions and contracts, which usually specify one or the other. When a document says "days", count days with this calculator; when it says "months", use the same day of the later month.
How do I count days between dates in Excel or Google Sheets?
Subtract the earlier date from the later one: =B1-A1 gives the days (format the cell as a number). =DATEDIF(A1,B1,"Y"), "M" and "D" give whole years, months and days, and =NETWORKDAYS(A1,B1) gives working days. This calculator uses the same conventions as DATEDIF.