Most weekly car rental rates have a 5-day minimum, and say so somewhere on the contract. More precisely, the rental period must be at least four full 24-hour periods and some part of a fifth. The reason for this is to prevent people renting during the week (business travelers) from booking a weekly rate, which is often lower than four (or even three) weekdays. If the minimum is stated on the contract, it's cut and dried. If Alamo charges you an extra $30 or whatever, that might be a lot less than four weekdays retroactively at "full rack". OTOH, if you are on a daily rate and bring the car back early, you are usually not charged for the days you do not use. For example: you rent a car for nine days, which is 1 week + 2 extra days. Bring it back on day seven and you're usually only charged for the week.