Date Calculator
Select two dates to see the difference between them. You can also add or subtract days from any date.
Number of days between two dates
Tuesday, March 31, 2026
Select both dates
Add or subtract days from a date
Date Calculator — Days, Weeks, and Months Between Dates
The date calculator is a versatile tool for finding the exact time between two dates or calculating a future/past date by adding or subtracting days. Results are displayed in days, weeks, months, and even business days.
How Does the Date Calculator Work?
The calculator computes the difference between two dates using calendar arithmetic. It handles varying month lengths (28–31 days), leap years, and the Gregorian calendar rules. The core conversion:
- Days — Exact number of days between the two dates
- Weeks — Days divided by 7
- Months — Approximate, using the average month length of 30.44 days
- Business days — Weekdays only (Monday–Friday), excluding weekends
Common Uses
| Scenario | How to Use |
|---|---|
| Project deadline | Enter start and end dates to see how many working days you have |
| Payment terms | Add 30, 60, or 90 days to an invoice date |
| Lease duration | Calculate exact months between move-in and move-out dates |
| Event countdown | How many days until a wedding, birthday, or vacation |
| Travel visa | Check if your visa covers your entire trip duration |
| Contract terms | Verify notice periods and renewal dates |
| Shipping estimates | Add business days to a ship date for estimated delivery |
| Age verification | Calculate exact days between two birth dates |
Adding or Subtracting Days
The second mode of the calculator lets you start from any date and add or subtract a specific number of days. The result includes the target date and the day of the week.
Examples:
- January 15 + 90 days = April 15 (Tuesday)
- December 25 − 30 days = November 25 (Tuesday)
- March 1, 2024 + 365 days = March 1, 2025 (Saturday)
Days in Each Month — Quick Reference
| Month | Days | Month | Days |
|---|---|---|---|
| January | 31 | July | 31 |
| February | 28 / 29 | August | 31 |
| March | 31 | September | 30 |
| April | 30 | October | 31 |
| May | 31 | November | 30 |
| June | 30 | December | 31 |
Leap year rule: A year is a leap year if it is divisible by 4, except century years — unless also divisible by 400. So 2000 was a leap year, but 1900 was not. 2024 is a leap year; 2100 will not be.
Interesting Date Facts
- There are 365.2422 days in a solar year, which is why we need leap years.
- The Gregorian calendar was introduced in 1582 by Pope Gregory XIII to correct the drift of the Julian calendar.
- Doomsday Algorithm — A mental trick to determine the day of the week for any date, invented by mathematician John Conway.
Frequently Asked Questions
How many days are in a year?
A common year has 365 days. A leap year has 366 days. On average, accounting for leap years, a year is 365.2425 days.
How do I calculate business days between two dates?
Count only Monday through Friday. This calculator can show you weekday counts. For more precision, you would also need to exclude public holidays specific to your region.
What is the Julian date?
The Julian date is a continuous count of days since January 1, 4713 BC. It is used in astronomy, military operations, and food packaging (where it is a 3-digit day-of-year code).
How many weeks are in a year?
There are 52 weeks and 1 day in a common year (52 weeks and 2 days in a leap year).
Related Tools
- Days Until Christmas — Countdown to December 25
- Age Calculator — Calculate exact age from a birth date
- Pregnancy Calculator — Track pregnancy weeks
- Vacation Days Calculator — Plan your time off
- Calendar Tool — Browse months and view calendars
Sources
- US Naval Observatory: Calendar Information
- timeanddate.com: Date Calculator