Route reliability record

BWI→BOS

Baltimore to Boston

Flights: 3,556
Period: July 2025 to June 2026
Distance: 369 mi
Carriers: 3

This route sits in the middle of the pack with a C. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.6%. The late ones land about an hour behind schedule. That rests on 3,556 flights, of which Republic Airways flew 1,086 at 80.8% 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.

On time

74.8%

Arrivals under 15 minutes late, of 3,457 completed flights

Avg delay

68 min

Across delayed arrivals only, not all flights

Cancelled

2.70%

National rate is 1.81%

Best carrier

Republic

80.8% on time across 1,086 flights

These figures cover 3,556 flights between July 2025 and June 2026. Beyond the headline rate, 9.4% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.

Carrier by carrier

Which airline is most reliable on BWI to BOS

The choice of carrier is not cosmetic here. Republic Airways arrives on time 80.8% of the time; Southwest Airlines manages 72.4%. Sample sizes sit next to every figure, because a two-point gap across 2,372 flights means less than a ten-point one.

On-time performance by carrier on BWI to BOS
Airline	Flights	On time	Avg delay	Cancelled	Grade
Republic Airways	1,086	80.8%	84 min	3.13%	B−
Southwest Airlines	2,372	72.4%	63 min	2.36%	C
Spirit Airlinesthin sample	98	68.5%	64 min	6.12%	C−

Republic Airways cancels 3.1% of what it schedules here, the highest in the table. A cancelled flight never appears in an on-time rate, so read that column alongside the punctuality one rather than after it.

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 40 points, against 8 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am557 flights92.0%
8am–11am720 flights90.4%
11am–2pm519 flights76.8%
2pm–5pm653 flights64.6%
5pm–8pm497 flights52.5%
8pm–5am610 flights67.2%

Scale runs 45% to 95%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 52.5% on time, against 92.0% 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 720 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 25 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.

Darker means more delays. Figures are on-time percentages.November best, September worst

November is the best month on the calendar at 85.1% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. July was the busiest month here, with 365 flights.

Across the week, Saturday is the strongest day at 82.6% on time and Sunday the weakest at 68.8%. 14 points is a smaller lever than departure hour, but it is free.

Delay causes

Why this route gets delayed

Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 59,000 reported delay minutes.

National Airspace System
39%
Carrier
29%
Late-arriving aircraft
29%
Extreme weather
2%
Security
0%

39% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 23,000 minutes out of 59,000, against a national NAS share of 21%. The split is drawn from 59,002 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 92.0% on time here.

Cancellations run at 2.70%, against 1.81% nationally. That is about one flight in 40 cancelled outright. A cancelled flight is invisible in every on-time figure on this page, so the punctuality numbers above describe only the flights that actually operated.

Connections and stage length

What a delay here actually costs

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 9.4% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.

At 369 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 5am–8am window matters as much as it does.

The return leg is a different operation and performs like one: it runs 78.9% on time across 3,551 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.

The sample behind these figures is 3,556 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. November runs 85.1% on time and September 60.2%, a swing of 25 points. If the dates move at all, move them out of September before you think about anything else. 3,457 completed flights over 12 months sit behind that.

Common questions

BWI to BOS questions

How often is BWI to BOS delayed?

About one flight in four arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 25.2% of the 3,556 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.

Which airline is most reliable on BWI to BOS?

Republic Airways leads at 80.8% on time across 1,086 flights. Southwest Airlines is at the other end on 72.4%, a gap of 8 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 BWI to BOS?

The 5am–8am departure window is the strongest at 92.0% on time. The 5pm–8pm window is the weakest at 52.5%, 40 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 September delays on BWI to BOS?

September is the weakest month at 60.2% on time, compared with 85.1% in November. Across the year that is 25 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.

Where to go next

Direction matters. BWI to BOS and BOS to BWI 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.

Key figures