Using Onedrive Excel for Service Charge Workbook

Hi all,

I am hoping if anyone as a minute to go over how to create a service charge workbook.

I need to have it include a weekly service charge of £15 and to have it update itself every week to add on an additional £15 but am unsure of the formula to input and how to begin the automatic update.

I have looked online for solutions and so far no options seem to be proving successful.

Many thanks for any help that can be provided

Regards,

Michael