formula for expiration date invoice

Hi,

I am using excel to create my invoices.

I have one cell with the creation date and one cell with the expiration date:

A21: Date created: 31-Aug-2011
A22: Expiration date:

I would like to use a formula to count 30 days from the date created to get the expiration date. So when i fill in the date created it automatically fills in the expiration date.

In this case the expiration date that should appear in cell A22 is 30-Sep-2011.

Is this possible?

Clausule

thanks. it works.

i have another issue in the same sheet. The cells that are used for USD amounts show the amount as:

$13,80

While it should be $13.80

When i go to Format Cells -> Number, i cannot change this.

When i go to File -> Options -> Advanced, Used system seperators is checked and showing Decimal seperator: . and Thousands seperator: ,

Why does it still not show the correct seperators in my cells?