Route reliability record
IAD→PWM
Washington to Portland
- Flights
- 801
- Period
- July 2025 to June 2026
- Distance
- 493 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 an hour and a half. That rests on 801 IAD to PWM flights, with a median arrival 12 minutes early.
Best time to fly IAD to PWM: a 8am–11am departure, ideally on a Saturday. Flights in that window arrived on time 95.6% of the time and Saturday flights 89.5%, against 87.6% 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 100 fewer late arrivals for every thousand flights.
Key figures
On time
87.6%
Arrivals under 15 minutes late, of 783 completed flights
Avg delay
91 min
Across delayed arrivals only, not all flights
Cancelled
2.25%
National rate is 1.81%
Best carrier
Republic
87.9% on time across 760 flights
These figures cover 801 flights between July 2025 and June 2026. The median arrival is 12 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 PWM
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 |
|---|---|---|---|---|---|
| Republic Airways | 760 | 87.9% | 94 min | 2.37% | A |
| United Airlinesthin sample | 41 | 82.9% | 52 min | 0.00% | B+ |
Best ways to make this trip
The most reliable ways to fly Washington to Portland
Every airline on this route and on the routes between nearby airports, ranked by how often a scheduled flight actually operated and arrived on time. 3 of the top 4 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. IAD → PWMWashington to Portland | Republic Airways | 85.8% | 87.9% | 2.37% | 8am–11am, Sat (route) | — |
| 2. BWI → PWMBaltimore to Portland | Southwest Airlines | 78.1% | 79.2% | 1.34% | 8am–11am, Wed | — |
| 3. DCA → PWMWashington to Portland | American Airlines | 68.3% | 69.9% | 2.29% | 8am–11am, Sat | — |
| 4. DCA → PWMWashington to Portland | PSA Airlines | 63.7% | 66.7% | 4.57% | 8am–11am, Sat | — |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
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 20 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am—
- 8am–11am185 flights95.6%
- 11am–2pm291 flights90.6%
- 2pm–5pm—
- 5pm–8pm184 flights83.3%
- 8pm–5am141 flights76.1%
Scale runs 70% to 100%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 95.6% of the time, against 76.1% for the overnight window. That is 20 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 11am–2pm window is the busiest, with 291 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 21 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 71.9% on time, against 92.9% in May. 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 123 flights.
The day of the week is close to irrelevant here: 4 points separates the best day from the worst. Weekly demand peaks are not what drives the delays on this operation.
Delay causes
Why this route gets delayed
One category carries most of the weight here. Carrier accounts for 42% of the 8,851 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.
- 42%Carrier
- 38%Late-arriving aircraft
- 16%National Airspace System
- 5%Extreme weather
38% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 8,851 reported delay minutes here, that single category outweighs weather by 8 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 8,851 reported delay minutes.
The largest share of delay minutes, 42%, 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 3,723 of the 8,851 delay minutes reported here.
Cancellations sit at 2.25% against a national 1.81%, which is ordinary. Diversions add another 0.00%.
Connections and stage length
What a delay here actually costs
Badly late arrivals are rare here: only 4.3% 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 493 miles this is a short hop, and stage length matters more than it looks. A flight this short spends under two hours in the air, which leaves almost nothing to claw back a late pushback with. Delay here is decided on the ground, in the turn, which is why the 8am–11am window matters as much as it does.
One caution: this is a thin sample. 801 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 PWM after this flight
What to do with this
Booking this route
Put together: treat all of this as provisional. 801 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 87.6% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 783 completed flights over 12 months sit behind that.
Common questions
IAD to PWM questions
How often is IAD to PWM 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 12.4% of the 801 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 PWM compared with the rest of the country?
87.6% 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 IAD to PWM?
The 8am–11am departure window is the strongest at 95.6% on time. The 8pm–5am window is the weakest at 76.1%, 20 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 IAD to PWM?
December is the weakest month at 71.9% on time, compared with 92.9% in May. Across the year that is 21 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
- Washington Dulles International (IAD) delay statistics
- IAD to ATL, a related route79.2%
- ORD to PWM, a related route74.0%
- IAD to DEN, a related route81.7%
- Republic Airways on-time record87.9%
- United Airlines on-time record82.9%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 million flight records
The reverse direction, PWM to IAD, is not among the 2,978 routes with a page of their own.
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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.