Date Calculator
Days between dates, add days to a date, age in days.
Difference
0 days
A date calculator answers common calendar questions: how many days are between two dates, what date falls a certain number of days from today, and how many weekdays lie in a span.
Enter two dates to get the difference, or a start date and a number of days to add or subtract. The tool accounts for month lengths and leap years automatically.
Counting days by hand is error-prone because months differ in length and February changes with leap years. The calculator removes both pitfalls.
How this calculator works
The calculator converts each date to a day count (a serial number of days) and subtracts to find the difference, which sidesteps uneven month lengths and leap years. Adding days works in reverse: it moves the serial number forward or backward and converts it back to a calendar date. Leap years, when February has 29 days, are handled by the standard rule (divisible by 4, except centuries unless divisible by 400). For business days, it counts only Monday through Friday across the span, optionally skipping holidays you specify.
What affects the number
- Whether you count inclusively or exclusively changes a span by one day.
- Leap years add a day to February and must be handled when a span crosses February 29.
- Business-day counts exclude weekends and, optionally, holidays.
- Month lengths vary, so day math is easier via a serial day count than by counting months.
- Time zones and daylight saving can shift which calendar day a moment falls on.
- Adding months is different from adding days, since months have different lengths.
Frequently asked questions
How do I calculate the number of days between two dates?
Subtract the earlier date from the later one. The calculator converts each date to a day count and finds the difference, automatically accounting for different month lengths and leap years, so you get the exact number of days.
How do I add days to a date?
Enter the start date and the number of days to add, and the calculator returns the resulting date. It carries across month and year boundaries and handles leap years, so adding 100 days to a date lands on the correct calendar day.
What are business days?
Business days are weekdays, Monday through Friday, excluding weekends and often public holidays. Counting business days is useful for delivery estimates, contracts, and deadlines, and this calculator can skip weekends and holidays you provide.
How are leap years handled?
A leap year has 366 days, with February 29 added. The rule is that years divisible by 4 are leap years, except century years, which must also be divisible by 400. The calculator applies this automatically when a span includes February 29.
This calculator provides general estimates for educational purposes only and is not financial, medical, legal, or tax advice. Your actual results depend on your specific situation and current rates.