How to Calculate the Number of Days Between Two Dates

Calculating the number of days between two dates comes up constantly: how many days until vacation or a deadline, how long a contract runs, how much time has passed since an event, how many full years old you are. Doing it by hand with a calendar is tedious — especially when the dates span different months or years with a leap February.

Why it's tricky by hand

Months have different lengths (28–31 days), there are leap years, and it's easy to make a mistake when crossing a year boundary. That's why it's more reliable to use a tool that accounts for all of this automatically.

How to calculate it online

Open the date calculator and choose the mode you need:

• Difference between dates — enter a start and end date and get the number of days (as well as weeks and months) between them.
• Date ± days — add or subtract a number of days from a date (handy for figuring out a deadline: "45 days from today").
• Age — how many full years, months, and days have passed since a birth date.

Everything is calculated right in the browser, nothing is sent to a server.

Common use cases

• Time left until an event — the difference between today and the event date.
• Contract term — the difference between the start and end date.
• Deadline — the "date + days" mode: for example, "payment due within 10 business days."
• Age — for forms and documents.

Whether to count the endpoints

An important detail: sometimes you need to include both endpoint dates, sometimes you don't. For example, "a 5-day term starting Monday" can be interpreted differently depending on the contract. The calculator shows the plain difference in days — whether to include the first or last day is up to you to decide based on the context.

For developers

If you work with dates in code or logs, converting a date to and from Unix time may come in handy — that's what the timestamp converter does.