Know before you go.

Spirit Airlines Baggage
Credit: Getty Images

There’s no avoiding it. Unless you plan on spending your vacation in the nude, or simply purchasing a new wardrobe while abroad, baggage is an essential (if sometimes aggravating) part of flying. And extra baggage fees are becoming more common than not.

But the more you know, the greater your chances of avoiding sticker shock. In our new series, we’re highlighting the various costs and policies associated with bringing luggage aboard a flight. First up, Spirit Airlines, whose handy online baggage calculator — coupled with a little extra planning — could help you save big.

What’s the deal?

If you’re a regular customer (and not a member of Spirit’s $9 Fare Club rewards program), and you reserve your baggage while you’re actually booking your Spirit Airlines ticket, the airline will only charge you $39 for a carry-on bag. It’s $32 for first checked bag, $42 for second checked bag, and $87 each for third, fourth, and fifth checked bag. All checked bags must be under 40 pounds, otherwise there are additional fees.

As always, any bag that’s carried on or checked must fit within the airline’s size requirements: those specific dimensions can be found here.

What’s the catch?

However, those fees go up the minute you start adding baggage to an already-confirmed flight ticket. For example, if you don’t get around to figuring out your luggage situation until after you’ve booked your ticket, you’ll pay $49 for a carry-on, $42 for a first checked bag, $52 for a second checked bag, and so on. If you wait until online check-in, those prices inflate by an additional $10—and if you happen to get caught reserving bags at the airport check-in counter, well, that’s an additional $10. In other words, when it comes to baggage, the longer you wait, the more you’ll pay.

Here’s another tip: Spirit’s baggage fees actually vary depending on the length of the flight, and when you’re flying. To help travelers calculate their expected baggage expenses, the Spirit Airlines website has a tool called the “Bag-O-Tron.” Simply enter your departure and arrival airport, along with projected travel dates, and the tool spits out the baggage fees that apply to your trip.

On Spirit, you’re not paying for a bag unless you need it,” clarifies Paul Berry, the airline’s corporate communications director. “We were the first airline in the US to say: ‘Actually, not everyone needs to check a bag; and if you don’t need to check a bag, you shouldn’t have to pay for it.’ Our method is more a la carte.”

What’s included?

A single personal item—which can range from a purse to a small backpack to a shopping bag—is included in a regular fare on Spirit Airlines.