Date Cell Drag Assist

Easy question I am sure. Searched all over Excell help with no luck before coming here.

I manage large and multiple spreadsheet on a weekly basis. Our reporting period is from Thursday to Wednesday. These are the past three date ranges:

1/04 - 1/10, 1/11 - 1/17, 1/18 -1/24.

When I execute the drag cell function the date defaults to the example below:

1/04 - 1/10 <----Cell that is dragged. 1/04 - 1/11 <-----Result of new cell.

What is the function or equation to have the above changed to below?:

1/04 - 1/10 <----Cell that is dragged. 1/11 - 1/17 <----Result of new cell.

Thanks so much. The answer will save about 15 minutes time. Maybe more.

Just tried entering the two first dates (a1 and a2), selecting both, and dragging the lower right handle and the result was obtained !