Route reliability record
SEA→DTW
Seattle to Detroit
- Flights
- 2,072
- Period
- July 2025 to June 2026
- Distance
- 1,927 mi
- Carriers
- 2
This route earns a B+. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 7 points better than the national rate of 77.6%. When something does go wrong the average delay runs about an hour. That rests on 2,072 flights, of which Delta Air Lines flew 1,532 at 85.3% on time.
Set against the rest of the country, this route's record is 7 points better than the US average of 77.6%. That gap is worth roughly 71 fewer late arrivals for every thousand flights.
Key figures
On time
84.7%
Arrivals under 15 minutes late, of 2,044 completed flights
Avg delay
59 min
Across delayed arrivals only, not all flights
Cancelled
0.82%
National rate is 1.81%
Best carrier
Delta
85.3% on time across 1,532 flights
These figures cover 2,072 flights between July 2025 and June 2026. The median arrival is 8 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.
Carrier by carrier
Which airline is most reliable on SEA to DTW
The two carriers here are closely matched: 2 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Delta Air Lines | 1,532 | 85.3% | 65 min | 1.04% | A |
| Alaska Airlines | 540 | 83.1% | 46 min | 0.19% | B+ |
No carrier stands out. Delta tops the table at 85.3%, 2 points clear of the bottom, which is inside the range this kind of sample moves year to year.
Departure window
The best time of day to leave
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 12 points, against 2 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am365 flights90.5%
- 8am–11am573 flights86.0%
- 11am–2pm352 flights78.4%
- 2pm–5pm222 flights87.3%
- 5pm–8pm—
- 8pm–5am560 flights82.6%
Scale runs 70% to 95%. Rows with fewer than 30 flights show a dash.
The weak window here is the middle of the day, not the evening: 11am–2pm runs 78.4% on time against 90.5% for 5am–8am. That shape usually means a departure bank rather than an accumulating delay, so the recovery later in the afternoon is real rather than noise. The 8am–11am window is the busiest, with 573 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 17 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.
August is the worst month at 75.0% on time, 17 points below October, the best at 92.4%. Summer afternoon convection and peak-season schedules land on the same weeks every year, so this is a pattern you can book around rather than a run of bad luck. July was the busiest month here, with 228 flights.
Across the week, Tuesday is the strongest day at 89.7% on time and Sunday the weakest at 80.1%. 10 points is a smaller lever than departure hour, but it is free.
Delay causes
Why this route gets delayed
One category carries most of the weight here. Carrier accounts for 50% of the 19,000 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.
- 50%Carrier
- 32%Late-arriving aircraft
- 15%National Airspace System
- 3%Extreme weather
- 0%Security
The largest share of delay minutes, 50%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 9,329 of the 19,000 delay minutes reported here. The split is drawn from 18,507 reported delay minutes.
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 90.5% on time here.
Cancellations are rare at 0.82%, below the national 1.81% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.
Connections and stage length
What a delay here actually costs
Badly late arrivals are rare here: only 4.0% land an hour or more behind schedule, against 8.1% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.
At 1,927 miles this is transcontinental flying, and long routes get a quiet structural advantage. Scheduled block time on a flight this length carries more padding in absolute minutes, so a twenty-minute late departure often still becomes an on-time arrival. Read the on-time rate here as slightly flattering next to a short-haul route with the same operational quality.
The return leg is a different operation and performs like one: it runs 73.2% on time across 2,076 flights, 12 points below this direction. Departure banks, aircraft rotations and the congestion at each end all differ, so scoring the two directions together would average away a real 12 points of difference.
The sample behind these figures is 2,072 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. October runs 92.4% on time and August 75.0%, a swing of 17 points. If the dates move at all, move them out of August before you think about anything else. 2,044 completed flights over 12 months sit behind that.
Common questions
SEA to DTW questions
How often is SEA to DTW delayed?
About one flight in seven arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 15.3% of the 2,072 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on SEA to DTW?
Delta Air Lines leads at 85.3% on time across 1,532 flights. Alaska Airlines is at the other end on 83.1%, a gap of 2 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.
What time of day has the fewest delays on SEA to DTW?
The 5am–8am departure window is the strongest at 90.5% on time. The 11am–2pm window is the weakest at 78.4%, 12 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.
How bad are August delays on SEA to DTW?
August is the weakest month at 75.0% on time, compared with 92.4% in October. Across the year that is 17 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- DTW to SEA — the return legseparate record
- Seattle-Tacoma International (SEA) delay statistics
- Detroit Metropolitan Wayne County (DTW) delay statistics
- Delta Air Lines on-time record85.3%
- Alaska Airlines on-time record83.1%
- The best time of day to fly, according to 7.04 million flight records
- Worst months to fly in the US, ranked by the data
Direction matters. SEA to DTW and DTW to SEA are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Updated monthly. How this data is collected.