When buying a ticket from an airline’s website or through a third-party agency like Expedia or Orbitz, you might not see what the cost of checking a bag is when viewing flight prices. It’s up to airlines if they want to display baggage costs, so the total ticket price you see might be less than what it actually costs. If you want to compare prices thoroughly between tickets, you’ll have to do some digging on your own to find baggage fees (airlines are still required to disclose details about ancillary fees on their website). If an airline doesn’t disclose its baggage fees and you’re checking a bag, you won’t know how much it costs until you enter your credit card information—or until you get to the airport.

Here’s how to get a free bag (or bags) on many of the major airlines.

• On American, the Citi/AAdvantage Platinum Select World Elite Mastercard includes the first bag free for the card holder as well as “up to four customers traveling with the eligible primary cardmember,” American says, as long as they’re on the same reservation. (The card’s $95 annual fee is waived the first year.)

•Alaska Airlines Visa Signature holders get a free bag plus one checked item for “six additional passengers in the same reservation.” This applies to Virgin America passengers through April, as well. (The card’s annual fee is $75.)

• The Gold Delta SkyMiles Credit Card lets you take the first bag free on all flights, plus the first bag for up to eight other travelers on the same reservation. (The card’s $95 annual fee is waived the first year.)

•United MileagePlus Explorer Card gives “the primary Cardmember and one companion traveling on the same reservation” a free checked bag each. (The card’s $95 annual fee is waived the first year.)

• The JetBlue Plus Card covers bags for “you and up to three travel companions on the same reservation, who have purchased Blue fares,” which are the airline’s most restrictive fares. The offer is good “on JetBlue-operated flights that do not include first checked bag free.” (The card has a $99 annual fee.)

• Spirit and Frontier, both notorious for charging for just about everything, do have branded cards—but they don’t cover baggage fees.

• Southwest, on the other hand, gives all passengers, including those that hold the Southwest Airlines Rapid Rewards Plus Card, two free checked bags on every flight. Now that’s a hack.