To make an international to international connection: 45 minutes. Incheon (ICN) is notoriously efficient for international connections—you should only need 45 minutes. You do not pass through customs or passport control, unless you are entering South Korea.

Whether you need to go through customs for a connecting flight at Seoul Incheon International Airport (ICN) depends on a key factor: whether your final destination is within South Korea or you are continuing to another country.

Here’s a simple breakdown:

1. International to International Connection (Most Common Scenario)

If you are arriving from another country and connecting to a flight to a third country (e.g., USA → Seoul → Thailand), you typically do NOT go through Korean customs or immigration. You will remain in the international transit area. You will not collect your checked luggage — it should be tagged through to your final destination. You simply follow signs for “Transfer”, go through a security screening for transit passengers, and proceed to your next departure gate.

2. When You DO Need to Clear Customs & Immigration:

You must enter South Korea (clear immigration, collect bags, clear customs) if: Your final destination is Seoul/South Korea. You are switching airports (e.g., landing at Incheon (ICN) and connecting from Gimpo (GMP) for a domestic flight). This requires entering the country and traveling between airports. You have two separate tickets (not booked on one itinerary) and need to collect and re-check your bags with the next airline. You are arriving on an international flight and connecting to a domestic Korean flight (e.g., USA → Seoul → Busan). In this case, you must clear immigration and customs at Incheon, collect your bags, and then re-check them for the domestic leg.