How to use the date calculator
Pick a tab, enter your dates and read the result. The tool works with calendar dates only, and all calculations happen in your browser.
What each mode does
Days between counts the full days separating two dates — useful for contract terms, project timelines, or figuring out someone's exact age in days. Days until counts down from today to a future date, or shows how many days have passed if the date is in the past. Add or subtract takes a starting date and shifts it forward or backward by a number of days — handy for deadlines like "30 days from the invoice date."
Worked examples
A note on how days are counted
This tool counts full calendar days between the two dates you enter, not including partial days or time of day. The end date is not counted as an extra day, so Monday to Friday of the same week shows 4 days. If you need to count both the first and last day, add 1 to the result. If you need business days only (excluding weekends), subtract roughly 2 days for every 7 in the result as a rough estimate, or count manually for exact figures around holidays.
Leap years
The calculator accounts for leap years automatically. A year is a leap year if it is divisible by 4, except century years, which must be divisible by 400. So 2028 is a leap year, 2100 will not be, and 2000 was. That is why the number of days between the same two calendar dates can differ by a day from one year to the next.
Common uses
- Payment terms and invoice due dates, such as net 30 or net 60
- Return windows, warranty periods and notice periods
- Project schedules and milestone planning
- Trip planning and counting nights between two dates
- Tracking how long ago something happened
For legal deadlines, check how the relevant rules count days, since some exclude weekends and holidays or include the start date.
Frequently asked questions
Can I add months or years?
This tool adds and subtracts days only. To find an exact age in years, months and days, use the age calculator.
Is there a live countdown?
Yes. The countdown timer shows days, hours, minutes and seconds to any date and updates every second. If the event happens in another time zone, convert the time with the time zone converter first.