Route reliability record
IAD→SLC
Washington to Salt Lake City
- Flights
- 714
- Period
- July 2025 to June 2026
- Distance
- 1,827 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 6 points better than the national rate of 77.6%. When something does go wrong the average delay runs an hour and a half. That rests on 714 IAD to SLC flights, with a median arrival 6 minutes early.
Best time to fly IAD to SLC: a 8am–11am departure, ideally on a Monday. Flights in that window arrived on time 91.8% of the time and Monday flights 87.0%, against 84.0% for the route overall.
Set against the rest of the country, this route's record is 6 points better than the US average of 77.6%. That gap is worth roughly 64 fewer late arrivals for every thousand flights.
Key figures
On time
84.0%
Arrivals under 15 minutes late, of 705 completed flights
Avg delay
92 min
Across delayed arrivals only, not all flights
Cancelled
1.12%
National rate is 1.81%
Best carrier
—
No carrier clears the floor
These figures cover 714 flights between July 2025 and June 2026. The median arrival is 6 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 IAD to SLC
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 |
|---|---|---|---|---|---|
| Delta Air Linesthin sample | 364 | 84.1% | 101 min | 1.65% | B |
| United Airlinesthin sample | 350 | 83.9% | 83 min | 0.57% | B+ |
Flight by flight
Flights on IAD to SLC
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 714 flights.
- 5am–8am364 flights84.1%
- 8am–11am49 flights91.8%
- 11am–2pm—
- 2pm–5pm—
- 5pm–8pm301 flights82.6%
- 8pm–5am—
Scale runs 75% to 95%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 91.8% of the time, against 82.6% for the evening window. That is 9 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5am–8am window is the busiest, with 364 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 22 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.
February is the weak month at 72.2% on time, against 93.7% in August. 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. August was the busiest month here, with 63 flights.
Across the week, Monday is the strongest day at 87.0% on time and Thursday the weakest at 80.0%. 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 59% of the 10,000 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.
- 59%Carrier
- 25%Late-arriving aircraft
- 14%National Airspace System
- 2%Extreme weather
The largest share of delay minutes, 59%, 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 6,150 of the 10,000 delay minutes reported here. The split is drawn from 10,385 reported delay minutes.
Cancellations sit at 1.12% against a national 1.81%, which is ordinary. Diversions add another 0.14%.
Connections and stage length
What a delay here actually costs
6.0% 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 last an hour and a half, which a normal layover absorbs.
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 87.5% on time across 713 flights, 4 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 4 points of difference.
One caution: this is a thin sample. 714 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 SLC after this flight
What to do with this
Booking this route
Put together: treat all of this as provisional. 714 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 84.0% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 705 completed flights over 12 months sit behind that.
Common questions
IAD to SLC questions
How often is IAD to SLC delayed?
About one flight in six arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 16.0% of the 714 flights in this analysis, against 22.4% nationally. Delayed flights are late by an hour and a half on average.
How reliable is IAD to SLC compared with the rest of the country?
84.0% of flights arrive on time here against a national 77.6%, a difference of 6 points in its favour. That is worth a B on this site's grading scale.
What time of day has the fewest delays on IAD to SLC?
The 8am–11am departure window is the strongest at 91.8% on time. The 5pm–8pm window is the weakest at 82.6%, 9 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 February delays on IAD to SLC?
February is the weakest month at 72.2% on time, compared with 93.7% in August. Across the year that is 22 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
- SLC to IAD — the return legseparate record
- Washington Dulles International (IAD) delay statistics
- Salt Lake City International (SLC) delay statistics
- Delta Air Lines on IAD to SLC84.1%
- United Airlines on IAD to SLC83.9%
- IAD to ATL, a related route79.2%
- DEN to SLC, a related route77.5%
- IAD to DEN, a related route81.7%
- Delta Air Lines on-time record84.1%
- United Airlines on-time record83.9%
- 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. IAD to SLC and SLC to IAD 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.