Counting days between dates by hand is a classic source of off-by-one errors: do you count the start day, the end day, both, neither? Contracts, notice periods, visa stays and project plans all hinge on getting this right, and "about three months" is not a number you can file.
Pick any two dates and this calculator gives the precise duration — total days, plus the breakdown in weeks, months and years — with a toggle for whether to include the end date. There is also a business-days count that skips weekends, for deadlines measured in working days.
Part of the Everyday Calculators collection on CountCrunch.
How the duration is counted
The calculator measures the exact calendar difference, accounting for leap years and months of different lengths:
Example: 1 January 2026 to 10 October 2026 is 282 days — 40 weeks and 2 days, or 9 months and 9 days.
Inclusive vs exclusive counting
Exclusive (default) counts the days strictly between the dates — the standard for "how many days until". Inclusive adds one, counting both endpoints — the standard for "how many days of leave" or rental days. A hotel stay from Friday to Sunday is 2 nights exclusive, 3 days inclusive. Pick the one your situation uses; getting this wrong is the most common date-math mistake there is.
Common uses
- Deadlines: days remaining until a filing date, exam or launch.
- Contracts: exact length of notice periods, leases and warranties.
- HR: probation periods, tenure and notice calculations.
- Personal: anniversaries, countdowns, "100 days since" milestones.
Frequently asked questions
How many days are between two dates?
Subtract the start date from the end date. The calculator above does it instantly, handling leap years and uneven months for you.
Do you count the start and end date?
It depends on context. "Days until" an event excludes the start day; "days of" something (leave, rental) usually includes both endpoints. Use the inclusive toggle to match your situation.
How many days is 3 months?
It varies: 89 to 92 days depending on which months. February to April is about 89 days; July to October is 92. Never assume 90.
How do I count business days between dates?
Count weekdays only, skipping Saturdays and Sundays (and holidays if relevant). The calculator has a business-days mode that does this automatically.