# Adding a Date/Time Interval in Excel

Posted by Roger Hyttinen on

One of the most common date calculations used is that of adding together a date and a date interval. For instance, if your customer invoices are due every 30 days, you would find the next due date by adding 30 to the last billing date. To add the number of days to a date, just use basic addition. For instance, if you wanted to add 30 days to today’s date, the syntax would be:

=TODAY + 30

### Adding Months & Years to a Date

If we want to add months or years to a date, the formula becomes a little more complex. To accomplish this, you will need to use the DATE function along with several arguments. Let’s say we wanted to add 6 months to today’s date. The format would be:

=DATE(YEAR(TODAY()),MONTH(TODAY())+6,DAY(TODAY()))

This formula is broken down as follows:

1. YEAR(TODAY()) – returns the Year portion of today’s date.
2. MONTH(TODAY())+6 – returns the Month portion of today’s date and adds 6 months to it.
3. DAY(TODAY())) – Returns the day portion of today’s date. The two closing parenthesis close the DATE part of the formula and the last argument, the MONTH part of the formula.

So if we wanted to add 45 days to the current date, our formula would read as follows:

=DATE(YEAR(TODAY()),MONTH(TODAY()),DAY(TODAY()) + 45)

Note: You may need to format the cell as a Date from the Format Cells dialog box as Excel will return the date in serial number format.