Time and Date Calculator

How to use the time and date calculator

Using the calculator is straightforward:

1. Enter your start date — this defaults to today, but you can change it to any date.
2. Choose whether to Add or Subtract time.
3. Enter the amount of time you want to add or subtract.
4. Select the unit: Days, Weeks, Months, or Years.
5. Click Calculate to see the resulting date.

The result shows the full date and day of the week, so you immediately know whether the date falls on a weekday or weekend.

Common uses for a date calculator

Date arithmetic comes up constantly in everyday planning. Here are some of the most frequent reasons people use a time and date calculator:

• Project deadlines: Find the exact due date when a project is due in 45 business days or 3 months from the start date.
• Contracts and leases: Calculate the expiry or renewal date of a lease, subscription, or service agreement that runs for a set number of months or years.
• Legal notices: Many legal processes require action within a fixed number of days of a triggering event. Calculate the exact deadline to avoid missing it.
• Pregnancy milestones: Add weeks to a conception or last menstrual period date to track milestones and estimate a due date.
• Warranties and guarantees: Find out when a product warranty expires by adding the warranty period to the purchase date.
• Event planning: Work backwards from an event date to find the date that is 30, 60, or 90 days before, for booking deadlines or preparation milestones.

Adding days vs adding months: what is the difference?

When you add days, the calculator moves forward exactly that many calendar days — simple and precise. Adding 30 days to January 15 gives February 14.

When you add months, the calculator moves forward by a calendar month, regardless of the number of days in each month. Adding 1 month to January 15 gives February 15. Adding 1 month to January 31 gives February 28 (or 29 in a leap year), since February does not have 31 days.

This distinction matters for contracts and billing cycles, which typically reference calendar months rather than a fixed number of days.

How to calculate a date in the past

To find a date in the past, choose Subtract in the operation field, then enter the number of days, weeks, months, or years you want to go back. This is useful for finding the start of a period — for example, what date was exactly 6 months ago, or what day of the week was 90 days before today.

Leap years and date arithmetic

The Gregorian calendar adds a leap day (February 29) every 4 years to keep the calendar aligned with Earth's orbit. The calculator handles leap years automatically. When adding years to a leap day date (February 29), the result in a non-leap year will land on February 28 — the last valid day of February — rather than throwing an error.

The full rule for leap years: a year is a leap year if it is divisible by 4, except for century years, which must be divisible by 400. So 2000 was a leap year, but 1900 was not.