One rental, many taxes

The add-on charges you'll encounter when renting a car vary widely in type, number, and cost, depending on location. Some add-ons are taxes, based on a percentage of rental price; others are fees, tacked on at a per-day or per-rental rate.

Some are imposed by states, on top of their usual sales taxes; some by counties, cities, or special taxing districts; and some by airports. Often two, three, four, or even five different taxes and fees will apply to each rental. Except for airport-imposed taxes, the add-ons generally apply no matter where you rent a car.

Really stiff airport taxes are a fairly new—and unwelcome—development. They've risen to 10 percent or more in quite a few major U.S. cities, as well as at several airports in Europe.

Dodging airport taxes
Can you avoid airport-imposed charges by renting off-airport? Usually not by going to a nearby, off-airport office: Most airports tax those rentals if the car company picks you up at the airport.

However, you can avoid the airport tax by renting at a downtown or suburban office. Figure your total expenditure before you decide on this tactic: On an inexpensive rental, the US$10 to US$40 you'd have to pay for a bus or taxi ride from the airport to a city rental office is more than you'd save by avoiding the airport tax. But if you're looking at a total rental bill of several hundred dollars, a downtown location may be a good choice (and you won't have to pay the tax even if you return the car at an airport).