The short answer is the price of a normal checked bag. On the five US airlines most of our riders use, that is $45 to $50 each way for the first bag. Not one of them charges a separate bicycle fee any more, and four of the five explicitly waive the oversize charge on a bike case. If you last flew with a bike a few years ago, this is worth rechecking, because the separate bike fee is gone.
What can still cost you real money is the scale. Every one of these airlines starts charging for weight at 50 pounds, and a packed bike case reaches 50 pounds faster than most people expect.
I read all five policies on the airlines' own pages while writing this. Here is where they stand.
What each airline charges to check a bike
American. A bike counts as a standard checked bag. Their wording: standard checked bag fees apply up to 50 pounds, the standard overweight fee applies from 50 to 70 pounds, and oversize fees do not apply. Maximum 115 linear inches and 70 pounds. First bag $50, or $45 if you pay online. Second bag $60, or $55 online. Basic Economy is $5 more per bag. Overweight is $30 from 51 to 53 pounds, then $100 from 54 to 70.
Delta. A bike is handled as standard checked baggage. It will not be accepted over 115 linear inches or at 100 pounds or more, and a bike over 50 pounds is charged the applicable excess weight fee. First bag $45, second $55. Delta's page does not say oversize is waived, so of the five this is the one to ask about at the counter. If the bike is not in a hard-shell case built for a bicycle, you sign a limited release of liability.
United. Their line is short: oversized fees are waived on properly packed bicycles. The bike counts toward your normal checked bag allowance. United publishes no bike-specific limit, so the general ceiling applies, 115 linear inches and 100 pounds. First bag $50, or $45 prepaid. Second $60, or $55 prepaid. Overweight is $100 from 51 to 70 pounds and $200 from 71 to 100.
Alaska. The most generous of the five. Oversize is waived up to 115 linear inches, and the overweight fee is waived up to 70 pounds, which none of the others do. First bag $45, second $55. Past 70 pounds the overweight fee applies at $200.
Southwest. Non-motorized bicycles with a single seat are accepted as checked baggage. Standard checked bag fees and overweight fees apply, oversize fees are waived. Hard cutoff at 115 inches and 100 pounds, above which they will not take the bike at all. First bag $45, second $55 on Basic, Choice and Choice Preferred fares. Southwest no longer includes a free bag on every fare, so check what yours covers before you assume the bike rides free.
Two things hold across all five. Nobody charges a bike fee. Everybody charges for weight.
The fee that catches people is weight, not the bike
Here is the arithmetic.
A common soft case, the Thule RoundTrip Pro XT, weighs 21 pounds empty. The EVOC Bike Bag Pro is close to it, about 19 pounds for the bag and around 22 with its stand and clip-on wheel. Put a 17 pound road bike in either one and you are at roughly 38 to 44 pounds before you have added a single other item.
Then the empty space gets filled, because it is right there and it is free. Shoes, helmet, tools, a pump, a spare tire, two sets of kit, the chargers. Each one is a pound or two, and the case crosses 50 without anyone ever deciding it should.
Crossing that line costs $100 on United and Southwest, $100 on American once you are past 53 pounds, and an excess weight charge on Delta. That is more than the bag fee itself, and on a round trip it is $200.
So weigh the case at home before you go. Stand on a bathroom scale holding it and subtract your own weight. If it reads 48 or more, take something out and move it to your suitcase, which is nowhere near its own limit.
Alaska is the exception. Up to 70 pounds it waives the overweight fee on a bike outright, and that is the single biggest difference between these five airlines.
One more thing the size numbers hide. A packed bike case is around 96 to 106 linear inches, which is far past the 62 inches a normal bag is allowed. That is exactly why the oversize waiver matters: without it you would be paying $200 on top of everything else, and it is the one part of this that airlines are quietly good about.
Costs that are not on the airline's page
The case. This is the real expense of flying with a bike, and it is a one-time one. If you expect to fly with a bike once a year, ask your local shop whether they rent travel cases before you buy one.
Tools and time, at both ends. All five airlines want the pedals off and the handlebars turned or removed. Southwest wants the handlebars removed. Alaska and United want them turned sideways. So you carry the tools, and you have to put the bike back together in a hotel room and take it apart again on the last morning. It is not difficult, but do it once at home first rather than learning it the night before your first ride.
Both directions. Every number above is one way.
Three things to do before you close the case
The airline's packing rules, pedals off and handlebars turned, are about getting the bike to fit. These three are about what happens to it once it is in there, and they are the difference between unpacking a bike that is ready to ride and unpacking a problem.
Take the rear derailleur off, or the hanger with it. The derailleur hangs off the most exposed corner of the bike, and that corner is what a dropped case lands on. A bent hanger will not shift cleanly, and straightening one properly takes an alignment gauge and a bench, which is not something to count on finding at the other end. Unbolt the hanger with the derailleur still attached to it, wrap the pair in a rag, and zip-tie it to the chainstay so nothing can swing. Two bolts, and the part that gets hit is no longer sticking out.
Put a spacer between the brake pads. With the wheels out there is no rotor holding the pads apart, and cases get stacked, squeezed and leaned on. One accidental squeeze of a lever on hydraulic disc brakes pushes the pistons together, and once they have closed up, the rotor will not slide back in until you reset them. A pad spacer, sold as a travel block or a transport block, sits in the gap and prevents it. They cost a couple of dollars, a new bike usually shipped with a plastic one in the box, and you want one for each brake.
Wrap the frame in pool noodles. The foam swim noodles from any supermarket, cut to length and split down one side, push straight onto a tube and stay there. Down tube, top tube, chainstays, and anywhere two parts of the bike would otherwise rest against each other. A few dollars, almost no weight, and it is what stands between a rub mark and a chip in the paint.
Shipping the bike instead of flying with it
Bike shipping services will take a boxed bike door to door and have it waiting at the hotel before you land. They price by box size and distance, so the only number worth having is a quote for your exact route and dates.
What you buy is usually not money. It is not dragging a 50 pound case through a connection, not gambling that your bike makes the same connection you do, and not needing a rental car big enough to swallow the case. If you are connecting, or renting something small at the other end, price it out. Send it early enough that a delay in transit is still not a delay for you.
When to bring your own bike and when to rent
Bring your own when the riding is serious, because fit is the one thing you cannot rent. Four days of climbing on a saddle that is not yours is an expensive way to learn that.
It is not the only answer, though. Many of our trips offer good rentals through a local shop, and each trip page lists what that trip has. For a shorter trip, or a flight with two connections, a quality rental from a shop that knows those roads is a fair trade.
Either way, the rest of what goes in the bag is its own list, and I wrote that one down separately: what to pack for a multi-day cycling tour.
If something does turn up damaged when you unpack at the other end, tell us. Someone on our team will look at it first, and where it needs more than that, we will find a local shop that can sort it. Doing the three things above is what keeps it from becoming the story of your first day.