Checked bag fees have quietly become one of the nastiest line items on a domestic flight. Alaska, American, Delta and United all now charge $45 to $50 for a first checked bag on US routes, Southwest has abandoned its famous 'bags fly free' policy with a $35 first-bag fee, and JetBlue's transatlantic bags start at $64. For a family of four doing a round trip, that's easily $300 or more before you've left the driveway.

The good news, as The Points Guy's roundup of 28 cards shows, is that nearly every major US airline has a credit card that waives the fee — and several cost under $100 a year, so a single round trip with a bag can pay for the card.

The most generous deals cover whole reservations. Alaska's Atmos Rewards cards (from a $95 annual fee) give a free first bag to you and up to six companions on the same booking. American's Citi AAdvantage Globe and Executive cards stretch to eight companions, as do five Southwest cards and Delta's lineup. Delta cardholders do even better on domestic flights: most of its cards include two free bags for the primary cardholder. United's Chase cards cover you plus one companion, with the Quest ($350) and Club ($695) cards covering two bags each. JetBlue's Plus and Business cards ($99) handle a first bag for you and three companions, and Frontier's World Mastercard throws in two free bags on every Frontier flight — remarkable value given the airline charges from $69 per bag on some routes.

A few catches are worth knowing. Most cards require you to actually buy the ticket with that card, and United and Delta also want your loyalty number on the reservation. The free bags usually don't stack: if you already get a free bag from elite status, a premium cabin fare or an international itinerary, the card won't add another one on top.

There's also a group-booking trap. Airlines typically price everyone on a reservation at the same fare, so if only three cheap seats remain and your fourth traveller pushes the whole booking into a higher fare class, you could pay $100 extra per person to save $70 per bag. Search in smaller groups before committing.

If you don't fly one airline often enough to justify a cobranded card, premium travel cards are the alternative: the Chase Sapphire Reserve offers $300 in annual travel credits, Amex Platinum gives up to $200 in airline fee credits with one chosen carrier, and Capital One's Venture cards let you erase travel purchases with miles at a penny each.

For anyone checking bags even two or three times a year on their usual carrier, the maths is simple: a $99 annual fee versus $70-plus per bag, per direction, adds up fast. Pick the card matching the airline you actually fly.