Wacharaklin/Getty Images

The biggest factors in finding the best lease deal are the term, monthly payment, and the amount due at signing, but to protect your wallet, you should dive deeper into the fine print. There are two other critical numbers to consider: the mileage cap, which is the maximum number of miles allowed before excess mileage fees accrue, and the cost per mile that you will have to pay at the end of the lease if you exceed that cap.

An annual mileage cap of 12,000 miles per year used to be the standard ­­– on a three-year lease, the mileage would be capped at 36,000 miles, for example – but recently there’s been a trend toward lower caps. Many leases from GM have caps of 32,500 miles on a three-year lease, while Ford has some 31,500-mile caps, and many luxury car deals have 30,000-mile caps over a three-year term.

So, what’s that really mean in terms of lease costs?

[Read Lease a Car Like a Pro]

To illustrate, we’ve picked two similar lease deals on cars with similar price tags. For our example, we found a Honda lease deal on the 2016 Civic EX sedan that costs $197 per month for three years with $2,017 due at signing. Over the term of the lease, you’ll pay $8,912.

We will compare it to a 2016 Chevy Cruze LT with the Preferred Equipment Package with a lease deal of $169 per month for 39 months with $2,499 due at signing. The Cruze will cost you $8,921 in lease costs over the life of the contract.

However, there’s a big difference in the cost you’ll pay per mile you drive. The Honda Civic lease allows you 36,000 miles over the lease term before excess mileage charges of 15 cents per mile begin to accrue. The Chevy lease costs 25 cents per mile for each mile you drive in excess of 32,500 miles.

DurdgenImages/Getty Images

If you were to return the cars at the end of the lease with precisely the maximum allowable mileage on the odometer, the Civic will have cost you 24.8 cents per mile, while the Cruze cost would be 27.4 cents per mile. That’s a significant difference, but it gets worse if you exceed the mileage cap.

That’s because for every additional mile in excess of 32,500 that you drive the Cruze, you’ll have to pay 25 cents per mile – that’s $250 for every 1,000 miles. If you were to drive the Cruze to the Civic’s 36,000-mile limit, you would have to pay Chevy $875.

The other number that you’ll want to give attention to is the rate at which the mileage cost builds. As we’ve already discussed, the Cruze costs 25 cents per excess mile, but Honda only charges 15 cents per mile for overages on the Civic. So the $250 extra that you pay for each thousand miles on the Cruze would only be $150 per thousand miles on the Civic.

[Read Can You Lease a Car With Bad Credit?]

This all underscores the fact that you need to fully understand your driving habits before you elect to lease. The best way to do so is to track the mileage on your current car to use as a predictor for your new leased car. If you can’t do that, look at the miles of your average commute, then add in an approximate number for the driving that you do in your off-time. It’s far better to be high on your estimate than to pay the punitive excess mileage costs.

In order to avoid extra fees at the end of your lease, you’ll also want to ensure that your daily driving tasks will not expose the vehicle to any significant damage. Those excess wear costs are added at the end of the lease, in addition to the mileage overage fees.

When you’re ready to lease, be sure to look at our lease deals page, where the experts from U.S. News & World Report research the market to find best lease costs each month. You can also learn how to avoid the seven top leasing mistakes and pick the right car for your lifestyle through our thorough rankings system. Stay up to date with the latest buying advice by following us on Twitter and Facebook.