Your total rental price is simply the car's daily rate multiplied by the number of rental days, calculated automatically when you book — no hidden surprises.
If you keep the car past the agreed return date, a late fee equal to the daily rate is added for each extra day, so it always pays to request an extension in advance if you need more time.
Returning the car on time, with the agreed mileage and fuel level, is the simplest way to keep your final bill exactly as expected.