Checking a bag on United Airlines can cost anywhere from nothing to several hundred dollars, and the difference usually comes down to four things: where you're flying, what fare you bought, your MileagePlus status and whether you carry the right credit card. Here's the rundown.

**Carry-on rules first.** Everyone gets one free personal item — a backpack, purse or laptop bag — as long as it fits under the seat (max 9 x 17 x 10 inches). A full-size carry-on (up to 22 x 14 x 9 inches) is free for most fares, but basic economy tickets generally allow only the personal item. Show up at the gate with a roller bag on a basic economy fare and you'll be checking it, paying the checked bag fee plus a $25 gate handling charge. Exceptions include flights to Canada, South America, across the Atlantic and Pacific, and MileagePlus Premier members with companions on the same reservation.

**Checked bags on domestic and regional routes.** For flights within North America, Central America and the Caribbean, a first checked bag costs $45 if you prepay at least 24 hours before departure, or $50 at the last minute. The second bag runs $55 prepaid, $60 after, and a third jumps to $200. Standard weight limit is 50 pounds per bag; elites and premium cabin passengers get 70.

**Long-haul is a different story.** Standard economy tickets to Europe and South America typically include one free bag (a second costs $100–$120), while Asia routes often include two free bags. Basic economy passengers usually pay around $90 for a first bag internationally. Africa and Australia itineraries generally include one free bag.

**Watch the weight and the odd-sized gear.** Overweight fees range from $100 to $300 for bags between 51 and 70 pounds, and $200 to $500 for 71 to 100 pounds — anything heavier is generally refused. Oversized bags over 62 linear inches start at $200 on top of the regular fee. Skis, snowboards and most sports equipment count as a regular checked bag with no surcharge, though don't bother bringing a kayak or canoe: United won't take them.

**How to skip the fees.** Every MileagePlus elite tier gets free checked bags on US and nearby international routes — Silver gets one free bag for you plus up to nine companions, Gold gets two, and Platinum, 1K and Global Services get three, all at the 70-pound limit. Star Alliance Gold members from other airlines get at least a first free bag too. Premium cabin tickets (Polaris, United Business, United First) include two free bags, and Premium Plus passengers get two at 50 pounds each. Certain United cobranded credit cards also unlock a free first bag and can cover the fee with statement credits.

The practical takeaway: if you're booking basic economy with a bag, do the math — the fare saving can evaporate fast. Prepaying bags 24 hours out saves $5 each, and status or the right card turns checked luggage into a non-issue.