Route reliability record
ATL→SEA
Atlanta to Seattle
- Flights
- 3,277
- Period
- July 2025 to June 2026
- Distance
- 2,182 mi
- Carriers
- 2
This route lands a B+, level with the national rate of 77.6%. Roughly one flight in five arrive 15 minutes late or worse, and those flights are late by roughly 55 minutes on average. That is a workable record, not a spotless one. That rests on 3,277 flights, of which Delta Air Lines flew 2,371 at 79.1% on time.
The US average over the same twelve months is 77.6%, so there is little to separate this route from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
77.8%
Arrivals under 15 minutes late, of 3,246 completed flights
Avg delay
54 min
Across delayed arrivals only, not all flights
Cancelled
0.64%
National rate is 1.81%
Best carrier
Delta
79.1% on time across 2,371 flights
These figures cover 3,277 flights between July 2025 and June 2026. The median arrival is 4 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 ATL to SEA
The two carriers here are closely matched: 5 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 | 2,371 | 79.1% | 53 min | 0.46% | B+ |
| Alaska Airlines | 906 | 74.3% | 55 min | 1.10% | C |
No carrier stands out. Delta tops the table at 79.1%, 5 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 19 points, against 5 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am628 flights83.5%
- 8am–11am680 flights80.0%
- 11am–2pm534 flights83.1%
- 2pm–5pm519 flights77.3%
- 5pm–8pm515 flights64.2%
- 8pm–5am401 flights75.9%
Scale runs 55% to 90%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 64.2% on time, against 83.5% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 8am–11am window is the busiest, with 680 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 28 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.
December is the weak month at 61.1% on time, against 89.0% in September. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days. July was the busiest month here, with 347 flights.
Across the week, Saturday is the strongest day at 81.9% on time and Monday the weakest at 74.6%. 7 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 39,000 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
- 27%National Airspace System
- 19%Late-arriving aircraft
- 5%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 19,000 of the 39,000 delay minutes reported here. The split is drawn from 38,746 reported delay minutes.
Cancellations are rare at 0.64%, 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
5.2% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route are the roughly 55 minutes kind, which a normal layover absorbs.
At 2,182 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 82.8% on time across 3,276 flights, 5 points above 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 5 points of difference.
The sample behind these figures is 3,277 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. September runs 89.0% on time and December 61.1%, a swing of 28 points. If the dates move at all, move them out of December before you think about anything else. 3,246 completed flights over 12 months sit behind that.
Common questions
ATL to SEA questions
How often is ATL to SEA delayed?
Roughly one flight in five arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 22.2% of the 3,277 flights in this analysis, against 22.4% nationally. Delayed flights are late by roughly 55 minutes on average.
Which airline is most reliable on ATL to SEA?
Delta Air Lines leads at 79.1% on time across 2,371 flights. Alaska Airlines is at the other end on 74.3%, a gap of 5 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 ATL to SEA?
The 5am–8am departure window is the strongest at 83.5% on time. The 5pm–8pm window is the weakest at 64.2%, 19 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 December delays on ATL to SEA?
December is the weakest month at 61.1% on time, compared with 89.0% in September. Across the year that is 28 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
- SEA to ATL — the return legseparate record
- Hartsfield-Jackson Atlanta International (ATL) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- Delta Air Lines on-time record79.1%
- Alaska Airlines on-time record74.3%
- 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. ATL to SEA and SEA to ATL 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.