Frontier Airlines, headquartered in Denver, is considered an “ultra low-cost carrier.” The airline offers extremely low fares that include only the flight — all other perks and amenities are considered “extras” and come with an additional charge. You pay for seat assignments, checked bags and even carry-on luggage and the in-flight food and drinks that come complimentary on many other airlines.

Frontier’s rationale is that they want to “unbundle” the airfare, letting you choose what you want to pay for. If you never check a bag, why should you have to pay the same cost as someone who does? This allows a minimalist traveler to get some incredibly cheap airfares. But before you fly Frontier, it’s important to understand what type of baggage and other fees you’re likely to be charged. That way you can have a complete picture of your total flight cost.

Frontier baggage fees: The basics

The only thing that comes free with your Frontier airfare is a small personal item that needs to fit under the seat in front of you.

The fees for carry-on luggage and checked bags depend on the route you’re flying, the date you’re flying, the weight of your bags and when you purchase your baggage allowance. You’ll always get the cheapest price by paying for your bags online at the time of booking. The price generally goes up the longer you wait, with the highest prices charged at the airport boarding gate. Frontier offers a bag fee-checker on their website, where you can see bag fees by searching for specific flights.

Here’s an example of the Frontier bag fees for checked and carry-on luggage for a flight between Cincinnati and Denver.

The cheapest price comes during booking and fees go up from there. Interestingly, the price for carry-on bags is more than the price for checked bags. That is opposite of most other airlines, where you might be used to only bringing a carry-on bag and not checking luggage in order to save on bag fees. With Frontier, if you need more than a small personal item, you may pay less by checking your bag instead of carrying it onboard the aircraft.

Different kinds of bags on Frontier

Frontier, like many airlines, divides bags by size into three categories:

Personal item: 8 inches deep by 18 inches wide by 14 inches high.

Carry-on bag: 10 inches deep by 16 inches wide by 24 inches high and less than 35 pounds.

Checked bag: 62 linear Inches (all dimensions added together) and less than 40 pounds.

According to Frontier's website, your personal item will be checked during boarding and is subject to an additional charge if it's larger. Frontier will also weigh and measure your checked bags when you check in, so make sure your checked bags meet the size and weight requirements.

Checked bags weighing 41-50 pounds will incur a fee of $50 per bag, per direction, while checked bags weighing 51-100 pounds will result in a $100 fee per bag, per direction. Bags over 100 pounds are not accepted.

It's important to note that Frontier's ticket counters close for check-in and bag drop 60 minutes prior to your flight's departure.

Also, if you are bringing only a personal item, depending on the flight attendants and how full the overhead bins are, you may be able to store your personal item in the overhead bin. That would allow you to free up some room for your feet in front of your seat.

Other Frontier fees

In addition to bag fees, Frontier also charges you to pick your seat — any seat. If you do not pay for a seat assignment, you will be assigned a seat when you check in. It has been my experience (although it is not guaranteed) that Frontier will seat you with other members of your party traveling on the same reservation if possible. The fees for seat selection depend on the flight and which seat you pick. A premium stretch seat or exit row will cost more than a middle seat in the back of the plane.

Remember that all bag and seat selection fees are per person and per flight. A round trip flight with four people will pay those bag and seat fees eight times. Your $19 airfare starts getting expensive pretty quickly!

Buying bundles: the Works and the Perks

Another way that you can save on your Frontier fees is by purchasing Frontier’s bundles. There are two types: one called the Works and another called the Perks.

Both bundles come with a carry-on bag, a checked bag and seat selection. Additionally, the Works bundle has zone 1 boarding, flight flexibility and 100% refundability, as well as the ability to purchase premium stretch seating. Prices for the Works and the Perks bundles vary by the route and dates of your flight. A good rule of thumb is that the cost should be around $60 to $120 per person for each leg of the journey.

Getting your Frontier baggage and other fees waived

There are a couple of ways to get your Frontier bag fees waived. The first is with Frontier elite status.

At Elite 20K, Frontier’s lowest level of elite status, you’ll get a carry-on bag for free. Top-tier Elite 100K members also get the Works bundle included for up to eight people on their reservation. Active-duty military members in uniform also get one free carry-on and two free checked bags.

In NerdWallet's most recent analysis of airline fees, we compared seat selection, checked baggage and overhead carry-on baggage fees charged by the major U.S. airlines on typical one-way fares. Here's how they stacked up:

The bottom line

When you’re eyeing an attractive low-cost flight on Frontier, remember that you may not be seeing your total cost. Baggage, seat selection and even soft drinks can add to the price of your trip. Factor in all the extras before you decide whether the fare is a good deal.