I'm in the UK now and have a Sixt rental car due back tomorrow.
It's a prepaid reservation if that makes a difference.

I think it likely that I'm going to be late dropping off the car, I asked a friend of mine who rents much more than I do and he said that it's not possible to extend the rental.

My question is what would I be charged if I'm a couple of hours late? I imagine that it's based on a daily rate, but what rate?

hotels have real-world rates and rack-rates, do car rental firms charge the extra day at a ludicrous rate or the rate you booked the car at.

any advice appreciated