# Date Calculator: Add or Subtract from a date

The Date Calculator can add or subtract days, weeks, months and/or years to or from a specified date, future or past.

Adding and subtracting dates using a calendar can be difficult and time consuming. A date calculator is an automated program used to add or subtract time to or from a specified date. Date calculators use programming functions and formulas to calculate time before or after a chosen date.

Information processed using our date calculator

• Past or future date after calculation
• Days, hours, minutes and seconds between two dates
• Leap years are also considered

## How to use the Date Calculator

1. Enter your chosen date. This is your start date or finish date.
Subtract Option: Date entered is your Finish Date.
The calculator will count back from this date.
3. Use the Day/Week/Month/Year buttons to enter the Days, Weeks, Months and/or Years you wish to add or subtract. You may enter as many or as few (at least one) time fields as you wish.
4. Click Calculate

### Example

Add 5 Days, 4 Weeks and 2 Years to January 1, 2017

1. Enter January 1, 2017
3.  Enter the following, using the Day, Week, and Year buttons: 5 Days 4 Weeks 2 Years
4. Click Calculate
5. Answer = February 3, 2019

## How Date Calculators Work?

A date calculator first needs to gather information including the initial date and time to be added or subtracted. Time is commonly represented as years, months, weeks and days. The best approach when adding or subtracting dates is to first sum the years, then months, then weeks and finally days. Each sum of time should be calculated separately and added separately to the date.

### Example

What is 1 year, 3 months, 4 weeks and 3 days from Jan 1, 2017?

Jan 1, 2017 + 1 year = Jan 1, 2018
Jan 1, 2018 + 3 months = Apr 1, 2018
Apr 1, 2018 + 4 weeks = Apr 29, 2018
Apr 29, 2018 + 3 days = May 2, 2018

= May 2, 2018

An alternate method to calculate a date in the past, present or future is to normalize the added time into a common time unit. Time units could all be represented as days and then added onto the initial date. Note: Avoid using this method when months are involved in the calculation unless you know the specific months and how long each month is.

### Example

1 year, 4 weeks and 3 days = 365 + 28 + 3 = 396 Days
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Proofs and formulas are provided as references.