We can apply formulas to calculate expiration dates in Excel easily. For example the start date is 8/14/2015 in Cell A2, and the expiration period is 3 months, here I will guide you to calculate the expiration date as follows:

1. Select a blank cell, type below formula into it, and then drag the Fill Handle to the range as you need.

=EDATE(B3,3)

2. Sometimes the calculated expiration dates may not display in date format. If so, please keep selecting the calculated expiration dates, and click the Home > Number Format drop down list > Short Date or Long Date. See screenshot:

Now the calculated expiration dates are showing in the proper date formatting.

Kutools for Excel's Date & Time Helper feature also provides an quite easy way to quickly calculate expiration dates in Excel. Please do as follows:

1. Select a blank cell for locating the expired date, and click the Kutools > Formulas Helper > Date & Time Helper to enable this feature.

2. In the opening Date & Time Helper dialog, tick the Add option in the Type section, specify the start date in the Enter a date or select a date formatting cell box, specify the expiration period as you need, and click the OK button.

Note: In my example, i suppose the expiration period is 3 months, therefore I enter 3 in the Month box in above dialog.

3. Keep selecting the formula cell, and drag its Fill Handle for applying this formula to the range as you need.

This Formula collection also provides formulas to calculate expiration dates if expiration period is measured with year, week, days, etc. See following screenshots:

If expiration period is 2 years:

If expiration period is 26 weeks:

If expiration period is 180 days:

If expiration period is 1 year 6 months and 20 days: