US domestic flights · Jan 2023 – Aug 2026

Why US flights run late

One in five arrivals lands at least 15 minutes late. Three questions about those delays: what causes them, when they happen, and where.

Arrivals delayed ≥15 min
21.1%
Arrivals cancelled
1.6%
Arrivals analysed
27.8M

Source: Bureau of Transportation Statistics, Airline On-Time Performance (delay cause). One record is one airline at one arrival airport in one month. “Delayed” means arriving 15 or more minutes late; cancelled and diverted flights are counted separately. 2026 covers January to August.

1What is the biggest cause of flight delays?

Late aircraft tops both measures, but it’s a knock-on effect. Trace it back and the airlines’ own operations cause most delays.

Two ways to measure “biggest”: both put late aircraft first
Each cause’s share of delayed flights and of delay minutes, Jan 2023 – Aug 2026
Share of delayed flights0%10%20%30%40%50%37.0%Late aircraft131.6%Carrier27.4%NAS33.8%Weather2,30.2%Security
Share of delay minutes0%10%20%30%40%50%40.5%33.6%19.7%6.1%0.2%
  1. 1Late aircraft is a symptom, not a cause: the inbound plane arrived late, so an earlier delay was passed down. Redistributed to the causes that started it, the root-cause split of delay minutes is Carrier 56% · NAS 33% · Extreme weather 10% · Security 0.3%.
  2. 2Extreme-weather delays are rare but long: 118 min each on average, vs 77 for carrier and 52 for NAS.
  3. 3BTS files non-extreme weather (rain, low cloud, wind) under NAS, so weather’s true share is understated. NAS = National Aviation System: air traffic control, airport congestion, heavy traffic.

Late aircraft accounts for 40% of delay minutes overall, but how much depends on the airline. Airlines that turn planes around quickly let one morning delay cascade through the rest of the day.

At five airlines, late aircraft causes over half of all delay minutes. At Hawaiian, Delta and SkyWest, the airline’s own operations are the main cause.
Share of each airline’s delay minutes caused by late aircraft vs by the airline itself, Jan 2023 – Aug 2026
  • Late aircraft
  • Carrier
0%10%20%30%40%50%60%half% delayedAir Wisconsin52%23%Frontier52%28%Southwest51%22%GoJet51%23%Piedmont51%17%PSA23%American25%Mesa19%Horizon17%Envoy20%CommuteAir17%Endeavor18%JetBlue27%Alaska21%United21%Allegiant24%Hawaiian57%19%Republic17%Delta46%18%Spirit25%SkyWest49%19%
  1. NAS, extreme weather and security make up the rest of each airline’s delay minutes. They are left out here to focus on the two causes that differ most between airlines.

2Which time of year is busiest, and does busy mean delayed?

Flight volume barely changes through the year, but delays nearly double from fall to summer. Summer is the worst season, not the holidays.

Volume varies by about 15%; the delay rate swings by about 70%
Each calendar month averaged across 2023–2026; faint lines show individual years
  • Average across years
  • Individual years
  • Notable event
Flights per day16k18k20k22k24k21,85219,018% of arrivals delayed ≥15 min0%10%20%30%27.7%16.0%Dec: delays up,flights down³% of arrivals cancelled0%2%4%3.4%0.6%CrowdStrike IT outage ’242Winter storms, Jan ’24 & ’261JanFebMarAprMayJunJulAugSepOctNovDec
  1. 1Winter storms (Jan 2024, Jan 2026): widespread cancellations. Jan 2026 is the highest month in the data at 4.8%.
  2. 2CrowdStrike IT outage (Jul 2024): a faulty software update took down airline IT systems on 19 July. Delta and Endeavor cancelled 6.6–8% of arrivals that month.
  3. 3Winter’s damage shows up as cancellations, which BTS does not count as delays. Read the bottom two panels together. December is where holiday travel shows: delays rise from 16% to 21% even as flights per day fall.

If busy meant delayed, the busiest months would also be the worst. They aren’t: volume and delay rate are only loosely related, and the gap from the Nov low (16%) to the Jul peak (28%) comes mostly from weather and stretched summer schedules.

October is as busy as May but has the fewest delays
Each dot is one month of one year. Correlation r = 0.40: busier months are only somewhat more delayed.
  • June – July
  • October
  • Other months
10%15%20%25%30%-10%-5%0%+5%Flights/day vs. that year’s average →OctoberJune – July
Every cause rises in June–July; extreme weather swings the most (×4.0)
Delay minutes per scheduled flight, average of each calendar month. Each panel has its own scale.
Late aircraftpeak / low ×2.30510JanAprJulOct
Carrierpeak / low ×2.005JanAprJulOct
Extreme weatherpeak / low ×4.001JanAprJulOct
NAS (air traffic & airport)peak / low ×2.20246JanAprJulOct

3Which airports experience the most delays?

Size doesn’t predict delays. San Francisco, Florida and San Juan run late more often than their airlines do elsewhere.

Counting delayed flights just ranks airports by size: the 30 busiest handle 64% of arrivals and 64% of delays, so a count map is really a population map. Every chart below applies at least one of four fixes:

  1. 1Rate, not count% of arrivals delayed
  2. 2Volume floordrop or shrink small, noisy airports
  3. 3Airline-mix adjustmentcompare to what its airlines do nationally
  4. 4Cause fingerprintairspace limits vs extreme weather
Showing 55 of 374 airports

Filters apply to every chart in this section. The floor removes airports with too few arrivals for a stable rate. Shrinking keeps every airport but blends its rate with the US average (21.1%) in proportion to how little data it has: an airport with 171 arrivals moves halfway, while ATL barely moves. The strength (k ≈ 171 arrivals) is estimated from the data. Shrinking adjusts rates (charts 1–3); the cause rankings (chart 4) are unshrunk. Turn both off to see the noise that both fixes deal with.

Fixes 1 + 2 · rate, with a volume floor
San Juan, San Francisco and Florida have the highest delay rates
15 highest % of arrivals delayed ≥15 min, Jan 2023 – Aug 2026
0%10%20%30%SJU San Juan27.8SFO San Francisco27.6PBI West Palm Beach26.0FLL Fort Lauderdale25.9MCO Orlando24.6SAN San Diego24.5JAX Jacksonville24.2BOS Boston24.0TPA Tampa23.9DCA Washington23.2MKE Milwaukee23.1MIA Miami23.0SAT San Antonio22.9LAS Las Vegas22.8MSY New Orleans22.8US avg 21.1%
Fix 2 · why a rate isn’t a population map
Bigger airports aren’t more delayed
Arrivals (log scale) vs % delayed. Correlation r = -0.11: close to none.
  • ≥3 pts above US average
  • ≥3 pts below
  • Within 3 pts
15%20%25%30%100k1MArrivals, Jan 2023 – Aug 2026 →US avgSJUSFOSLCPBIFLLIADMSPMCOATLSANBOIJAXPDXORDDFWDEN

Some airports share a high delay rate because they share airlines. The next chart compares each airport with what its own airlines achieve nationally in the same month. What remains is the airport’s own effect.

Fix 3 · airline-mix adjustment
SFO stands out: about 7 points worse than its airlines manage elsewhere
Percentage points above or below what each airport’s airlines achieve nationally in the same month
  • Worse than its airlines
  • Better than its airlines
−10−50+5+10SFO San Francisco+6.8PBI West Palm Beach+3.2SAN San Diego+3.1SJU San Juan+2.8JAX Jacksonville+2.5MKE Milwaukee+2.3FLL Fort Lauderdale+2.3BOS Boston+2.0LGA New York+1.9DCA Washington+1.8EWR Newark+1.7ORD Chicago+1.5MSP Minneapolis−1.6BUR Burbank−1.8MDW Chicago−1.9PDX Portland−2.1BWI Baltimore−2.2OAK Oakland−2.2IAD Washington−2.5PHX Phoenix−2.6SJC San Jose−2.8CLT Charlotte−2.9SNA Santa Ana−3.4SLC Salt Lake City−4.1
  1. Several big hubs beat their own airlines’ national average. ATL has the most arrivals in the data and sits at −1.6 pts. Rankings are fairly stable from year to year (rank correlation 0.55–0.76), so this isn’t noise.
Fix 4 · cause fingerprint
Newark, SFO and New York lose the most time to air traffic; Dallas, Chicago and the upper Midwest to extreme weather
Delay minutes per arrival from each cause: the 10 highest airports for each. Each panel has its own scale.
Air traffic & airport (NAS) · min per arrival02468EWR Newark7.9SFO San Francisco7.0LGA New York5.7BOS Boston5.1FLL Fort Lauderdale5.1PBI West Palm Beach5.1ORD Chicago4.9JFK New York4.9MCO Orlando4.7DCA Washington4.4US avg 3.0
Extreme weather · min per arrival00.511.52DFW Dallas–Fort Worth1.8ORD Chicago1.4DTW Detroit1.3MSP Minneapolis1.2MKE Milwaukee1.2DCA Washington1.1CLT Charlotte1.0LGA New York1.0PHL Philadelphia1.0CVG Cincinnati1.0US avg 0.9
  1. NAS = air traffic control, runway capacity and congestion: the delay cause an airport has the most control over. 38% of SFO’s delay minutes are NAS: fog and closely spaced parallel runways cut its arrival rate. EWR and LGA also have the highest cancellation rates (about 3%).