Based on everything I've gathered, here's the best answer I can give you: # How to Add a Bag to a United Flight Once the Flight Is in Your Cart **The short answer:** On united.com, bags are added on the checkout ("Review and pay") page — the same page where your selected flight appears in the cart. If you've already passed that step or already paid, you add bags afterward through **My Trips**, the **United app**, or at **check-in/airport**. ## During booking (flight already in cart) After you select your flight and fare class on united.com, you land on the checkout page where your itinerary is shown. On that page, each traveler has optional add-ons — look for the **"Bags"** section/link for each traveler and set the number of checked bags before entering payment. If you don't see a bag option on that page (this happens on some Basic Economy fares and certain international/codeshare itineraries), United will tell you to add the bag after purchase or pay at the airport. ## After you've already paid (most common path) If you've completed the purchase, add the bag here: 1. **united.com → "My Trips"** → open your reservation → find the **"Add baggage"** / bag option → choose the number of bags per traveler → pay. 2. **United app** → Trips → your flight → **"Add bags"** (same function as the website). 3. **Online check-in** (opens 24 hours before departure) — add bags then. 4. **At the airport** — self-service kiosk or check-in counter (this is usually the most expensive option). ## Key timing & cost notes - **Prepay at least 24 hours before departure** to get the lower online price (e.g., ~$35/bag online vs ~$40 at the airport for domestic). After that window, you pay the standard airport fee. - **Basic Economy** typically does **not** include a free carry-on or checked bag — you must pay separately. - **Some international itineraries don't qualify for prepaid bag purchase** — United will tell you to pay at the airport, and the fee is usually the same as online. - **Fees vary by route, fare class, and destination** — always check the current fee schedule on United's site or app. ## What I could not verify I was unable to open United's official pages directly (united.com blocks automated access), so the exact on-screen labels of the in-cart bag step couldn't be confirmed from United's own site. The steps above are based on third-party guides and user reports; if the bag option isn't visible on your checkout page, the reliable fallback is to complete the purchase and add the bag via **My Trips** or the **app** before check-in. **Sources I opened:** - [EasyInfoHub — How to Add Bags on United Airlines](https://easyinfohub.com/how-to-add-bags-on-united-airlines/) (pre-paying via My Trips/app, 24-hour window, fee differences, Basic Economy rules) - [United Airlines — Checked Bags page](https://www.united.com/en/us/fly/baggage/checked-bags.html) (official page, but content was JS-blocked in this browser) - [Reddit r/unitedairlines — "Purchase checked bag before flight"](https://www.reddit.com/r/unitedairlines/comments/1cpk0u4/purchase_checked_bag_before_flight/) and ["Cutoff to pre-pay for baggage online"](https://www.reddit.com/r/unitedairlines/comments/1ceygrh/cutoff_to_pre_pay_for_baggage_online/) (user reports that the bag option isn't always visible during checkout, and that prepay must be done ≥24h before departure) — note these pages were JS-blocked when I tried to open them directly, so I only have their search snippets.