Date Calculator: Days Between Dates & Date Math
How many days until a project deadline? How long has a contract been running? How old will someone be on a specific date? These questions sound simple but calendar arithmetic β with varying month lengths, leap years, and timezone considerations β is surprisingly easy to get wrong. A date calculator gets it right every time.
Common Use Cases for Date Calculation
Project deadlines
How many days remain until the launch date?
Contract durations
When does a 90-day notice period end from today?
Age calculation
How old is someone born on a specific date?
Travel planning
How many days between departure and return?
Trial periods
When does a 30-day free trial expire?
Legal & finance
Payment is due 45 days after invoice date β what date is that?
Calculating the Difference Between Two Dates
The most common operation is finding the number of days between two dates. This sounds straightforward, but months have different lengths (28β31 days), and leap years add an extra day every four years (with exceptions for century years). The safest approach is to use a reliable tool rather than counting on a calendar manually β especially for durations spanning multiple months or years.
Results can be expressed as total days, or broken down into years, months, and days β useful for displaying ages or contract lengths in a human-readable format.
Adding or Subtracting Days from a Date
The second major operation is date arithmetic: start with a date, add or subtract a number of days, and find the resulting date. This is essential for:
- β’ Notice periods: Add 30, 60, or 90 days to today's date to find the end of a notice period
- β’ Payment terms: Net-30 invoices: add 30 days to the invoice date for the due date
- β’ Return windows: Subtract to check if a return is still within the 30-day window
- β’ Scheduling: Add 14 days for a follow-up meeting, 90 days for a quarterly review
A Note on Business Days
Calendar days vs. business days
Calendar day calculations (which this tool performs) count every day including weekends. If you need business days(MondayβFriday only, excluding public holidays), the result will differ. For example, "30 business days" from a Monday is approximately 6 calendar weeks. Always clarify whether a contract or deadline specifies calendar days or business days.
How to Use the Date Calculator
Choose your operation
Select 'Difference between dates' to count the days between two dates, or 'Add/subtract days' to find a future or past date.
Enter your dates
Pick dates using the date pickers or type them directly. The calculator handles month boundaries and leap years automatically.
Read the result
Get the answer in total days, and optionally broken down into years, months, and days for a more readable duration.
Calculate dates now
Difference Β· Add/subtract days Β· Leap year aware Β· Free Β· No sign-up
Open Date Calculator βFrequently Asked Questions
How do I calculate the number of days between two dates?
Subtract the earlier date from the later date. In most date calculators, enter a start date and end date and the tool computes the difference in days. For example, from January 1 to December 31 is 364 days (non-leap year). Our free date calculator handles all the math instantly.
How many days are in a year?
A regular (common) year has 365 days. A leap year has 366 days. Leap years occur every 4 years (years divisible by 4), except for years divisible by 100 that are not divisible by 400. So 2000 was a leap year, but 1900 was not.
How do I add days to a date?
To add days to a date, enter the starting date and the number of days to add. Our calculator handles month boundaries, year boundaries, and leap years automatically. For example: January 20 + 30 days = February 19 (or 20 in a leap year).
How many weeks between two dates?
Divide the number of days between the dates by 7. For example, 100 days Γ· 7 = 14 weeks and 2 days. Our date calculator shows the difference in days, weeks, months, and years simultaneously.
What is a Unix timestamp?
A Unix timestamp is the number of seconds elapsed since January 1, 1970, 00:00:00 UTC (the Unix epoch). It's used by computers and APIs to represent a point in time as a single integer. For example, the Unix timestamp 1717200000 represents June 1, 2024.