Time for connecting flight

Barely, if you are lucky.

• It is not customs that takes time (it takes no time). It is immigration (passport control), which takes 30-90 minutes. In rare horror cases longer. Immigration takes place before you collect your luggage.
• A transatlantic flight could arrive late, for technical reasons or because the wind is blowing in the wrong direction (or it could be early).
• Transfer between terminals: 20 minutes (no stopping for a toilet break or anything else).
• Make sure you pay for your hold bags when you buy your tickets. With Easyjet it costs more if you pay for your bags at check-in.
• Complete your easyJet check-in and print your boarding card before you leave home. You can do it 30 days in advance.
• Easyjet has self-service bag drop off. Deposit your bag, and go straight to security.
• Easyjet has a strict check-in time limit. You must be at the gate 40 minutes before departure. They are not flexible on this limit.
  • See here (click on "Important timings" at the bottom): https://www.easyjet.com/en/help/boarding-and-flying/boarding-and-on-board-services

richard, is your easyJet flight a true connection meaning you're flying on the "worldwide by easyJet" product in which you will be flying a partner airline across the Atlantic and then connecting on easyJet so that it is all on one ticket?

If it is not a connecting flight & you miss your easyJet flight, you will have to buy new tickets. If the easyJet flight is a roundtrip between Gatwick and Belfast, you will have to buy new roundtrip tickets because by missing the outbound, you cancel the inbound back to Gatwick.

If you are flying on the "worldwide by easyJet" product, contact easyJet before you leave to find out the process of getting listed on the next available flight to Belfast if you miss your flight. Find out if you will need to use your phone to call a customer service center, go to an easyJet ticket window for the agent to find available seats on a future flight, or will easyJet book you automatically and let you know via their app as soon as you arrive and have access to wifi? It will save you time having this info long before you leave.

3 hours is too tight because besides the risk of your inbound being late, long lines at immigration, and easyJet's strict gate arrival rule of 40 minutes before departure that Chris F wrote above, you are choosing to check your luggage. You will lose valuable time, particularly if your transatlantic flight is late, by waiting to pick up your bags at the baggage carousel.

Consider flying with carryon only if you choose to keep this itinerary.

Do you really want to be eating Tums non stop on your trans-Atlantic flight, hoping it works?

I suggest you explore a "Plan B"