Route reliability record
SLC→IAD
Salt Lake City to Washington
- Flights
- 713
- Period
- July 2025 to June 2026
- Distance
- 1,827 mi
- Carriers
- 2
This route earns an A. Close to nine flights in ten arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 10 points better than the national rate of 77.6%. When something does go wrong the average delay runs about an hour. That rests on 713 SLC to IAD flights, with a median arrival 8 minutes early.
Best time to fly SLC to IAD: a 8am–11am departure, ideally on a Tuesday. Flights in that window arrived on time 91.1% of the time and Tuesday flights 92.2%, against 87.5% for the route overall.
Set against the rest of the country, this route's record is 10 points better than the US average of 77.6%. That gap is worth roughly 99 fewer late arrivals for every thousand flights.
Key figures
On time
87.5%
Arrivals under 15 minutes late, of 703 completed flights
Avg delay
66 min
Across delayed arrivals only, not all flights
Cancelled
1.26%
National rate is 1.81%
Best carrier
—
No carrier clears the floor
These figures cover 713 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 SLC to IAD
Only one carrier clears this site's 365-flight floor here, so there is no comparison to draw. The table below is the full picture.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlinesthin sample | 349 | 89.0% | 70 min | 0.86% | A+ |
| Delta Air Linesthin sample | 364 | 86.0% | 63 min | 1.65% | A |
Flight by flight
Flights on SLC to IAD
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
Departure window
The best time of day to leave
Departure time is the single lever a traveller controls, and it moves the odds more than most people expect. Each bar below is the on-time rate for flights scheduled to leave inside that window, across 713 flights.
- 5am–8am—
- 8am–11am216 flights91.1%
- 11am–2pm52 flights82.7%
- 2pm–5pm—
- 5pm–8pm361 flights85.9%
- 8pm–5am84 flights88.0%
Scale runs 75% 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 82.7% on time against 91.1% for 8am–11am. 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 5pm–8pm window is the busiest, with 361 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 23 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.
July is the worst month at 72.6% on time, 23 points below August, the best at 95.2%. 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. January was the busiest month here, with 62 flights.
Across the week, Tuesday is the strongest day at 92.2% on time and Sunday the weakest at 81.6%. 11 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 56% of the 5,836 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.
- 56%Carrier
- 21%National Airspace System
- 19%Late-arriving aircraft
- 4%Extreme weather
The largest share of delay minutes, 56%, 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 3,269 of the 5,836 delay minutes reported here. The split is drawn from 5,836 reported delay minutes.
Cancellations sit at 1.26% against a national 1.81%, which is ordinary. Diversions add another 0.14%.
Connections and stage length
What a delay here actually costs
Badly late arrivals are rare here: only 4.6% 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 1,827 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 84.0% on time across 714 flights, 4 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 4 points of difference.
One caution: this is a thin sample. 713 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.
Work out the risk of missing a connection in IAD after this flight
What to do with this
Booking this route
Put together: treat all of this as provisional. 713 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 87.5% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 703 completed flights over 12 months sit behind that.
Common questions
SLC to IAD questions
How often is SLC to IAD delayed?
About one flight in eight arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 12.5% of the 713 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
How reliable is SLC to IAD compared with the rest of the country?
87.5% of flights arrive on time here against a national 77.6%, a difference of 10 points in its favour. That is worth a A on this site's grading scale.
What time of day has the fewest delays on SLC to IAD?
The 8am–11am departure window is the strongest at 91.1% on time. The 11am–2pm window is the weakest at 82.7%, 8 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 July delays on SLC to IAD?
July is the weakest month at 72.6% on time, compared with 95.2% in August. Across the year that is 23 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
- IAD to SLC — the return legseparate record
- Salt Lake City International (SLC) delay statistics
- Washington Dulles International (IAD) delay statistics
- United Airlines on SLC to IAD89.0%
- Delta Air Lines on SLC to IAD86.0%
- SLC to DEN, a related route77.8%
- ATL to IAD, a related route76.5%
- SLC to PHX, a related route83.9%
- United Airlines on-time record89.0%
- Delta Air Lines on-time record86.0%
- 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. SLC to IAD and IAD to SLC are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.