According to MyBaggageInfo, United’s checked baggage allowance for most domestic U.S. flights is one bag free for Medallion members, military, and eligible cardholders; otherwise, the first bag costs $35 and the second $45 (online prepay saves a few dollars). Bags must be under 50 lbs and 62 linear inches. Overweight (51–100 lbs) adds $100–$200; oversize (63–115 inches) $200. International rules vary widely by region—many routes include one or two free bags. Always check United’s baggage calculator for your exact itinerary.