These days, according to Jonathan Weinberg, co-founder of car rental discount site AutoSlashpeople rent cars at the last minute as often as they reserve ahead.

Last-minute plans increasingly fit the way we live now. But that doesn't mean last-minute prices are always cheaper.

"Because rental car companies tend to set their prices based on inventory in each location, they reward those who book earlier because it allows them to plan," says Liana Corwin, travel expert for booking engine Hopper.

So how can you make sure you get a good deal if you book at the last minute? We asked some of the top industry experts.

Book on the right day of the week.

"Check your rates on Tuesdays, if you can," advises Mark Mannell, CEO of Car Rental Savers. "The car rental agencies have some last-minute rates that they tend to upload on Tuesdays for the coming week, which can save you some money."

If your travel falls around holidays, note that some days will be far more expensive than others for picking up a car. "Prices and crowds tend to be lower for pick-ups that start on the Friday or Saturday before Thanksgiving,” says Nisreene Atassi, Global Head of PR and Social for Expedia.

He notes that rentals starting the Wednesday before the Thanksgiving holiday tend to cost 30% more. For Christmas, he says that those who start rentals on December 25 tend to pay the highest rates.

Pick up and drop off at the right hour.

Car rentals are done in 24 hour “chunks,” says Hopper's Corwin, so you'll pay the least when you pick up and drop off the car at the exact same time of day. If you input times that are mismatched by a few hours, you risk being charged for an entire additional day.

She notes that most agencies have a grace period, and you can use that to avoid paying for an extra day. If your desired pick-up and drop-off times fall within the same few hours and your drop-off time is the later of the two, reserve a pick-up time that's for the same hour as your expected drop off. You can usually show up an hour or two ahead of your reservation time without a penalty or higher rates.

Play the field.

Mannell of Car Rental Savers notes that there is never a single agency that’s always the cheapest. Rates depend on supply and demand, and that will vary based on the date of your rental, and the location.

Hopper, a site that predicts the ideal time to book airfares, recently started aggregating rental car rates, and its results cover a broad spectrum of renters from small agencies to multinational companies. Car Rental Savers and AutoSlash are notable for applying discount coupons of all sorts to the rental car costs they show customers. We’ve also found that Priceline and Hotwire can be good sources for last-minute deals on car rentals.

Compare the prices for on- and off-airport rentals.

Because of the fees charged by airport concessions, rentals near the terminal tend to be pricier than those off-airport. The extra fees can even cost more than a taxi or Uber from baggage claim to the rental desk.

But there are no hard-and-fast rules. Mannel notes that during off-peak times, airport agencies often have more cars in the lot than city-based agencies do, so airports will sometimes charge lower prices simply because they have so much more inventory to move. So it's always important to check both in-town and airport prices, just in case.

Never show up without a reservation.

"Walk-up rates are typically set each day by the rental office's local managers," says AutoSlash's Weinberg. "Unless they're nearly sold out, they will choose a middle-of-the-road rate that is usually higher than what the reservations department has set."

Hopper's Corwin notes that the prices for optional add-ons such as rentable GPS systems and insurance tend to be cheaper online, too.

Remember the additional expenses.

Speaking of GPS systems and insurance, all of our experts stress that it’s crucial to consider all of the expenses you’ll incur from your rental car, and to do so before you get to the check-in counter.

Prices to check ahead of time include gas mileage for different classes of cars, extra fees for second drivers (some agencies allow spouses to drive for free; others don’t), charges for GPS systems, and more.

Car companies also thrive on selling travelers insurance they don’t need, so be sure to see what your regular insurance policy and/or credit card already covers—in fact, your existing coverage may require you to decline the insurance offered at the car rental desk. Remember: Those smiling faces behind the counter may be working on commission.

Some other key ways to cut miscellaneous costs:

• Return your car with a full tank. That will always be less expensive than letting the rental car company fill the tank, even if you buy a pre-paid option for it.

• Rent a toll pass. Some U.S. state highway departments allow cross-border use of the transponder or tag you might use in your car at home. Other states may offer passes you can borrow for short visits. But if you forget and accidentally go through a cashless tollbooth without making preparations, most rental car agencies tack on high fees to the price of tolls.

Enroll in loyalty programs.

A basic membership is free and joining usually only involves a few minutes on the rental agency's website.

The benefits are real: Members are often offered discounts and promotions that aren’t available to the general public.

Belonging to the agency's membership program might also give you priority over another potential last-minute renter if there's a shortage of cars on the lot—something that happened frequently in 2020 as renters culled their fleets due to low demand.