Date Calculator
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Enter your details and hit “Calculate” to see your results.
About the Date Calculator
Two everyday date problems, one tool. First: how far apart are two dates — for deadlines, lease terms, subscription periods, project timelines, or a countdown to an event? Second: what date lands a given number of days, weeks, months, or years before or after a known date — for notice periods, return windows, warranty expirations, or medication schedules?
Both modes work on the real calendar: months keep their true lengths, leap days appear exactly where the leap-year rules put them, and every result names the weekday, because “30 days from now” is more useful when you know it’s a Sunday.
Measuring from a date of birth instead? The Age Calculator
How Days Between Dates Are Counted
The duration mode reports the same gap three ways — total days, weeks plus leftover days, and calendar years/months/days:
Total days = End date − Start date (end date not counted) Weeks = Total days ÷ 7, remainder shown as days Years / months / days = calendar breakdown, borrowing from real month lengths
Worked example: January 1, 2026 to July 10, 2026 is 190 days — 27 weeks and 1 day, or 0 years, 6 months, 9 days. The end date isn’t counted, so a Friday-to-Friday week is 7 days, not 8. If your use case counts both endpoints (days of a rental including pickup and return day), add 1 to the result.
Adding & Subtracting Dates
Days and weeks are exact arithmetic: 30 days after July 10, 2026 is Sunday, August 9, 2026, and 2 weeks before July 10, 2026 is Friday, June 26, 2026. Months and years move to the same day number in the target month — and when that day doesn’t exist, the result clamps to the month’s last day: January 31, 2026 + 1 month = February 28, 2026, and February 29, 2024 + 1 year = February 28, 2025.
That clamping rule is the convention used by banks for monthly billing dates and by spreadsheet EDATE functions, so results here line up with statement dates and contract anniversaries. If you need “last day of each month” behavior instead, start from the 1st of the following month and subtract a day.
Days in Each Month
Month lengths are why date math needs a calculator — a quick reference:
| Month | Days | Month | Days |
|---|---|---|---|
| January | 31 | July | 31 |
| February | 28 (29 in leap years) | August | 31 |
| March | 31 | September | 30 |
| April | 30 | October | 31 |
| May | 31 | November | 30 |
| June | 30 | December | 31 |
Leap years: divisible by 4, except century years that aren’t divisible by 400 — 2024 and 2028 are leap years, 2026 isn’t; 2000 was, 1900 wasn’t. A common year has 365 days, a leap year 366.
Calendar Days vs Business Days
This tool counts calendar days — every day including weekends and holidays, which is what leases, interest, visas, and most legal deadlines use. Business-day counting excludes weekends and public holidays, which differ by country and even by state or province. For a quick estimate, every full week contains 5 business days (190 calendar days ≈ 27 weeks ≈ 135 business days, before subtracting holidays); for anything contractual, check the specific holiday calendar that applies.
Frequently Asked Questions
How do I calculate the number of days between two dates?
Count the days from the start date up to, but not including, the end date. By hand you’d add up the remaining days in the start month, the full months between, and the days into the end month; the calculator does this on the real calendar, leap days included, and also shows the answer in weeks and in years/months/days.
Does the count include the end date?
No — the standard convention counts nights, not days: Monday to Friday is 4 days. If your situation counts both endpoints (for example, days a library book is out including the day borrowed and the day returned), add 1 to the result.
What is one month after January 31?
February 28 — or February 29 in a leap year. When the target month is shorter than the starting day number, the result clamps to the last day of that month. This matches how banks schedule monthly payment dates.
How are leap years handled?
The calculator uses the real Gregorian rules: a year is a leap year if divisible by 4, unless it’s a century year not divisible by 400. So 2024 and 2000 are leap years; 2026 and 1900 are not. February 29 appears exactly where the calendar puts it.
Can this count business days?
It counts calendar days. To approximate business days, multiply full weeks by 5 and subtract public holidays for your region — holiday calendars vary too much for a one-size-fits-all count.
What’s the difference between this and the age calculator?
Same math, different framing: the age calculator fixes the start date at a birth date and adds birthday-specific extras (birth weekday, next-birthday countdown), while this tool handles any two dates plus add/subtract operations.
Methodology. This calculator uses standard, peer-reviewed mathematical formulas. It is reviewed and maintained by the Vast Calculators editorial team.
Last updated · July 2026
Results are estimates for general use; verify critical figures independently.