Date Difference Calculator
Calculate the exact difference between two dates — with working days option
How Date Difference Is Calculated
The total number of days is calculated by subtracting the start date from the end date. Working days are counted by iterating through each day and skipping Saturdays and Sundays. The "include end date" option adds 1 to the total (useful when counting both the first and last day of a period).
Years, months and days are calculated the same way as age — the years component counts complete years, then remaining months and days. This gives an exact human-readable breakdown rather than a simple division.
Counting Days Between Dates: Harder Than It Looks
Built and verified by Andrius R. · Updated June 2026
"How many days between two dates" sounds like subtraction — and it is, right up until the fence-post problem, the business-day question, and the legal fine print. Here's where day-counting goes wrong and how to get it right.
The fence-post problem: inclusive vs exclusive
Exclusive (subtraction, what this calculator and spreadsheets do): 12 − 8 = 4 days — the number of day-steps between the dates. Right for "how long until," durations, and ages.
Inclusive (counting both endpoints): 5 days — Mon, Tue, Wed, Thu, Fri. Right for "how many days does this cover": hotel-style nights vs rental-style days, medication courses, billing periods.
Neither is wrong; they answer different questions. The classic check: from a date to the same date is 0 days exclusive — if your situation insists that's "1 day," you need inclusive counting. Off-by-one errors from mixing these up are so universal they're named after fence posts: ten fence sections need eleven posts.
Calendar days vs business days
June 2026 has 30 calendar days but only 22 working days — weekends remove roughly 2/7 of any span, and public holidays (which vary by country and even region) remove more. This matters because deadlines specify one or the other: courts and contracts often run on business days, visas and returns policies usually on calendar days, and "5–7 business days" shipping quietly spans up to 11 calendar days over a weekend-and-holiday stretch. The calculator's working-days mode handles weekends; for holiday-exact legal deadlines, check the jurisdiction's official list — and note many legal systems also roll deadlines landing on a weekend to the next working day.
Why you can't just multiply years by 365
A 30-year span contains about 10,957 days, not 10,950 — leap days accumulate (roughly 7 in any 30-year window). The rule itself has two exceptions stacked on it: every 4th year is a leap year, except century years, except centuries divisible by 400 — so 2000 leaped, 2100 won't. This is why precise spans (interest accrual, pharmacology, astronomy) are computed by actual date arithmetic, never by years × 365. Banking adds its own twist: bonds and loans use day-count conventions like 30/360 (every month pretends to have 30 days) or Actual/365, and the same loan can accrue measurably different interest under each — when a contract mentions a day-count basis, that fine print is this exact problem.
Quick answers to the common cases
- "90 days from 15 January 2026" = 15 April 2026 — and note 90 days ≠ 3 months: three calendar months from 15 January is also 15 April here, but from 30 November it's 28 February vs 2 March (one definition follows the calendar, the other counts 90 exact days). Visa rules that say "90 days" mean days, not months.
- A full year, 1 Jan to 31 Dec = 364 days exclusive — the inclusive count, 365, is the one that matches intuition. Fence posts again.
- Weeks between dates: divide the day count by 7; the remainder tells you the weekday shift — useful for "what day of the week is it 100 days from now" (100 = 14 weeks + 2 days → two weekdays later).
- Age in days: a surprisingly pleasing milestone generator — your 10,000th day lands around age 27⅓; pair it with the age calculator for the exact date.
// Working Days
The "working days" count excludes Saturdays and Sundays but does not account for public holidays, which vary by country.
// Include End Date
If you want to count both the first and last day (e.g. "from Monday to Friday inclusive = 5 days"), tick "include end date".
// Project Planning
For project timelines, use working days. A "2-week project" typically means 10 working days, not 14 calendar days.
// Deadline Counting
Legal deadlines often use calendar days. Contract deadlines may specify "business days". Always check which counting method applies.