What is the most common cause of flight delays?

The most common cause of flight delays in the US is late-arriving aircraft, which accounts for roughly 40% of all delays. This happens when a plane that was supposed to fly your route is delayed on its previous flight. Weather is the second leading cause at about 25%, followed by airline operations (crew, maintenance, boarding) at 20%, and air traffic control congestion at 15%.

Are morning flights less likely to be delayed?

Yes. Early morning flights (before 8 AM) have significantly higher on-time rates than afternoon or evening flights. This is because delays cascade throughout the day — a plane that runs late on its 7 AM departure will be late for its 10 AM, 1 PM, and 4 PM flights too. Booking the first flight of the day gives you the best odds of departing on time.

Which airline has the fewest delays?

Among major US airlines, Delta Air Lines consistently ranks highest for on-time performance, followed by Alaska Airlines and United Airlines. Budget carriers like Frontier and Spirit tend to have lower on-time rates. However, performance varies significantly by airport and route, so always check the specific airport and airline combination for your flight.

How accurate is this flight delay calculator?

This calculator uses historical data from the Bureau of Transportation Statistics (BTS), which tracks every domestic flight operated by major US airlines. It shows you the actual on-time performance based on millions of real flights. While past performance doesn’t guarantee future results (a snowstorm can change everything), historical rates are the most reliable predictor of overall delay patterns at an airport.

Flight Delay Calculator

What's the chance your flight is late? Check any airport and airline using real federal delay data.

Enter your departure airport and optionally your airline. We'll show you the on-time rate, average delay length, cancellation rate, and the main reason flights run late there — all based on millions of real flights tracked by the DOT.

Check your delay risk

What causes flight delays

About 20% of US flights are delayed in any given month. The causes break down roughly like this:

·Late-arriving aircraft (~40%) — your plane was delayed on its previous flight, so it arrives late to your gate
·Weather (~25%) — thunderstorms, snow, fog, and high winds at your airport or en route
·Airline operations (~20%) — crew scheduling, maintenance, boarding issues, or IT problems
·Air traffic control (~15%) — airspace congestion, ground stops, and runway capacity limits

Worst airports for delays

Some airports are consistently worse than others. The most delay-prone major airports in the US include:

EWR Newark SFO San Francisco JFK New York JFK ORD Chicago O’Hare LGA LaGuardia

See the full worst airports ranking →

Worst times to fly

Delays follow a predictable pattern through the day:

·6–8 AM: Best on-time rates. Planes start fresh.
·12–3 PM: Delays start stacking up from morning issues.
·4–8 PM: Worst window. Afternoon thunderstorms + cascading delays from earlier in the day.

See the best time to fly analysis →

Delays by airline

On-time performance varies significantly between airlines. Legacy carriers like Delta and Alaska tend to perform better overall, while budget airlines like Frontier and Spirit have lower on-time rates. But the picture changes by route and airport — use the calculator above to check your specific combination.

See the full airline delay rankings →

Delays Today Worst Airports for Delays Best Time to Fly Airline Rankings