What days of the week is your car rental?
I will give you a scenario when they will take a day off.

If you rent Monday-Thurs (3 week day rental) and you return it a day early, you should get credit for a week day.

If you if you rent Friday-Sunday and you return it early, then you SHOULD get a day credit as this is a weekend rental.


However, if you rent for 5 days, which is a weekly rental, and decided to return a day early, then this can and should change your rate, often higher as it is calculated as 4 daily rates, which may be higher than a weekly rate.

Also, if you rent a Wed, thur, and Friday, and you return it early, you should get credit for a third day.

I speak from my own experiences with Hertz, as I now rent exclusively from them, so I can't be sure for other rentals.

Hope this helps.