Date Calculator
Find the difference between two dates, or add and subtract days from a date.
What This Date Calculator Does
This tool handles the three date calculations people need most often: finding how many days lie between two dates, adding a number of days to a date, and subtracting a number of days from a date. It's useful for planning deadlines, tracking countdowns, or working out due dates.
How It Works
The difference calculation counts the exact number of calendar days between your two chosen dates and also converts that into weeks. The add and subtract tools move a start date forward or backward by the number of days you specify, giving you the resulting calendar date.
Frequently Asked Questions
Does the date difference include both start and end dates?
The calculator reports the number of days between the two dates. If you need an inclusive count (counting both the start and end day), simply add 1 to the result.
Can I add more than 365 days?
Yes, you can add or subtract any whole number of days, including values well over a year.
What happens if I enter the end date before the start date?
The calculator still shows the number of days between them and notes that the end date comes before the start date.
How to check this result
Use the calendar picker instead of typing an ambiguous date format.
Method and assumptions
The days-between result measures the distance between two dates. Adding days moves forward from the start date; subtracting days moves backward.
Before making a decision
If a deadline counts both the first and final day, check whether an inclusive count is required.
Calendar days versus working days
Method and inputs
The difference between two dates counts elapsed calendar days. Adding days advances the calendar by that count; subtracting days moves backward. Calendar-day calculations include weekends and public holidays.
Worked example
From 1 January 2026 to 10 January 2026 there are nine elapsed days. Counting both endpoint dates as included calendar dates gives ten. Adding ten days to 1 January reaches 11 January.
Limits and common mistakes
State whether the start date counts before using a result for a deadline. A contract may use business days or local holiday rules that this calendar tool does not apply. Month lengths and leap years matter when entering dates.
Does it count daylight-saving hours?
Calendar dates and elapsed hours are different measurements. Use a time-zone-aware timestamp calculation when you need actual hours across a daylight-saving change.
Content updated: 2026-10-03.