Copying row to the last empty row and add a new date based on cell value

[a94andwi]

Hello

I am trying to create a preventive maintanance calendar and I'd like to add activities to a list and set the first inital date in one cell.
When the user has performed the activity they write which date is was performed on and a the row is copied to the last empty row in the list.
A new date is written based on the "Days to next activity"-value.

I have attaced a excel file with the basic idea.
Can anyone help me with the macro code since I am really poor on this.

/Anders