Layover Time Calculator

Layover time planning is the difference between a smooth connection and a missed flight. This calculator factors in arrival time, terminal distance, customs clearance, and gate availability to assess whether your connection is safe.

Minimum connection time (MCT) formula: Available Connection Time = Layover Duration − Buffer Risks Buffer Risks = Arrival Delay Risk + Terminal Change Time + Customs Time + Walk/Transit Time + Security Re-entry Time

Minimum safe layover times by scenario:

Why a domestic-to-international connection needs longer, and it is not customs. Leaving the United States you clear no immigration and no customs. There is no exit control, so nothing happens to you between the two gates except the walk. What eats the time is the boarding cutoff: international flights close the door earlier, typically 45 to 60 minutes before departure against 15 to 20 for a domestic hop, because the crew has to reconcile the passenger manifest against the advance passenger information the destination country requires. A connection that would be fine domestically can leave you standing at a closed gate 40 minutes before an international departure.

Worked example: Flight arrives 2:15 PM. Connecting flight departs 4:10 PM. Available time: 115 minutes, which is 1.92 hours in the box above.

It is an international arrival onto a US domestic flight, same terminal, and the bags have to come off the belt and go back on. Add the steps up:

So 115 minutes against 150 needed. The calculator calls that Too Tight, High Risk and puts the buffer at minus 35 minutes. It is not unmakeable, and people do make it every day, but you are relying on the inbound landing early and no queue at passport control. Book the later connection if there is one.

Two of those rows are worth arguing with. The 30-minute arrival buffer is the reason this figure runs above the airline’s own minimum connection time: an airline builds its MCT assuming the inbound is on schedule, and yours might not be. And the 45 minutes at immigration is an average that Global Entry cuts to near zero, which on this itinerary would take the minimum down to about 105 and turn the whole answer around.

Red flags that increase miss risk:

• First flight frequently delayed (check FlightAware stats)
• Weather-sensitive departure city (Chicago, Denver, Dallas in winter)
• Separate airline bookings (you bear the rebooking cost)
• Busy hub airports with long walks (DFW, LAX, JFK Terminal changes)

Rule of thumb by airport size:

• Small regional airport: 30 min often fine for domestic
• Medium hub (Boston, Seattle): 60–75 min domestic
• Large hub (LAX, JFK, ORD): 90–120 min domestic; 3+ hours international