How the days between two dates are counted
By default the calculator counts the number of days from the start date to the end date, the same way you would count nights in a hotel stay: from Monday to Friday is 4 days. If you need to count both the first and last day — for example, the length of an event or a vacation including both travel days — tick Include the end date, which adds one day. Leap years are handled automatically, including February 29.
Business days
Business days count Monday through Friday and skip Saturdays and Sundays. They're used for shipping estimates, legal and contract deadlines, payment terms and notice periods. Public holidays vary by state, province and employer, so subtract any holidays that fall in your date range from the business-day count shown. In the U.S. there are 11 federal holidays a year; in Canada, statutory holidays differ by province, with most provinces observing 9 to 10.
Adding or subtracting days
Switch to Add / subtract days to find the date a certain number of days in the future or past — useful for return windows, warranty periods, probation periods, medication schedules or "90 days from today" deadlines. Enter a negative number to count backwards. With business days only ticked, weekends are skipped, so 10 business days from a Monday lands on the Friday of the following week.
Common date questions
- How many days in a year? 365, or 366 in a leap year. A year is a leap year if it is divisible by 4, except century years, which must be divisible by 400 — so 2000 was a leap year and 2100 will not be.
- How many weeks in a year? 52 weeks plus one day (two in a leap year).
- How many business days in a year? About 260–262, before subtracting holidays.
To find someone's exact age in years, months and days, use our age calculator. For Canadian citizenship applications, which require counting days of physical presence, try the citizenship calculator.
Everyday uses
People use a date calculator for many practical reasons: counting down to a wedding, vacation or retirement date; checking how many days remain on a lease, warranty or free trial; working out notice periods when changing jobs; tracking pregnancy milestones in weeks; or calculating interest for a specific number of days. Businesses use it for invoice due dates such as "net 30" or "net 60" terms, project timelines and service-level deadlines. Because months have different lengths, counting by days is the most precise way to measure any period, and converting to weeks or months afterwards avoids common off-by-one mistakes.