For over a month I used a rental car for business use while my car was being repaired, how do I add that mileage for my business miles?

[AlanT]

If you rent a vehicle for business purposes, you can deduct the full cost as a business expense. Under this circumstance, you are probably better off not taking the mileage deduction, because it may not save you as much money as writing off the full cost of renting the car. For example, you may have taxes, insurance, and fuel costs added to the base rental rate. You can't write off the full cost of renting a vehicle and the mileage as well. You must choose one or the other.

[dediwood]

I did not pay a rental fee.  It was paid for with insurance from a car wreck.  It was used while my car was in the shop.