How Much Layover Time Do You Actually Need?

Airlines sell connections on their minimum connection time, not on whether the inbound flight arrives in time to make them. Here's how to read the real misconnection risk from the arrival record.

By Eric, OnTimeIndex Founder · Last reviewed July 2026

When a booking engine offers you a 40-minute connection, it is telling you the connection is legal — not that it will work. Those are different claims, and the gap between them is where missed connections live.

Minimum connection time is a floor, not a forecast

Every airport-and-airline pair publishes a minimum connection time (MCT): the shortest gap the carrier will sell between an arriving flight and a departing one. It runs roughly 30 to 90 minutes for domestic connections. MCT accounts for the walk between gates and the bag transfer under ideal conditions — it assumes both your flights are on time. It is set by the airline and the airport, not the government, and it says nothing about how often the inbound flight actually arrives in time to use it.

The number that matters is your slack: your layover minus the MCT. A 90-minute layover with a 45-minute MCT gives you 45 minutes of slack — the inbound flight can arrive up to 45 minutes late and you still make the connection. Book a layover that only just clears the MCT and your slack is near zero, so any inbound delay at all breaks the trip.

The real risk is in the inbound flight’s arrival record

A connection fails when the first flight lands too late, so the honest way to size a layover is to look at how that inbound route has actually arrived over months of filings. The Department of Transportation records the arrival delay of every flight (14 CFR § 234.2). Line up the whole distribution of past arrivals and ask a simple question: what share of them would have arrived within your slack? That share is your historical connection success rate — a base rate, not a promise, but a far better guide than the fact that the itinerary is bookable.

Why a booked itinerary always looks better than it flies

A base rate from the arrival record is, if anything, optimistic about a specific trip, because it can’t see the frictions that push the wrong way:

A terminal change or a long gate-to-gate walk beyond what the MCT assumes.
Re-tagging bags or clearing security again on some itineraries.
A single delayed inbound aircraft that also delays your outbound — delay begets delay across a day.

None of those show up in the inbound arrival distribution, so treat a computed success rate as a ceiling. If it’s marginal, the fix is more layover, not optimism.

How to use it

The Connection Risk Calculator takes your connecting airport, your inbound route, your scheduled layover, and your own MCT — it doesn’t bake one in, because there isn’t a single correct value — and returns the share of historical inbound arrivals that would have made the connection. Set the MCT to your actual itinerary’s and you get a number grounded in what the route has really done, not in what the booking flow is willing to sell.

Sources

Try the Connection Risk Calculator →

Informational only — every figure here comes from historical federal filings, not a prediction of any future flight, and nothing here is professional travel advice.