Route reliability record

BOS→DTW

Boston to Detroit

Flights: 2,591
Period: July 2025 to June 2026
Distance: 632 mi
Carriers: 4

This route lands a B, level with the national rate of 77.6%. Roughly one flight in four arrive 15 minutes late or worse, and those flights are late by a little over an hour on average. That is a workable record, not a spotless one. That rests on 2,591 flights, of which Delta Air Lines flew 1,712 at 79.6% 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

77.6%

Arrivals under 15 minutes late, of 2,532 completed flights

Avg delay

75 min

Across delayed arrivals only, not all flights

Cancelled

2.12%

National rate is 1.81%

Best carrier

Delta

79.6% on time across 1,712 flights

These figures cover 2,591 flights between July 2025 and June 2026. Beyond the headline rate, 9.2% 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 BOS to DTW

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 79.6% of the time; JetBlue Airways manages 71.7%. Sample sizes sit next to every figure, because a two-point gap across 723 flights means less than a ten-point one.

On-time performance by carrier on BOS to DTW
Airline	Flights	On time	Avg delay	Cancelled	Grade
Republic Airwaysthin sample	1	100.0%	—	0.00%	A+
Spirit Airlinesthin sample	155	82.6%	62 min	0.00%	B+
Delta Air Lines	1,712	79.6%	77 min	2.04%	B
JetBlue Airways	723	71.7%	72 min	2.77%	C

Delta leads JetBlue by 8 points. Real, but small enough that a better departure time on the weaker carrier can outweigh 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 37 points, against 8 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am569 flights93.2%
8am–11am502 flights89.8%
11am–2pm433 flights79.0%
2pm–5pm280 flights64.6%
5pm–8pm410 flights69.0%
8pm–5am397 flights56.1%

Scale runs 50% to 100%. Rows with fewer than 30 flights show a dash.

The 8pm–5am window is where this operation falls apart: 56.1% on time, against 93.2% 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 5am–8am window is the busiest, with 569 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 18 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.September best, July worst

July is the worst month at 67.1% on time, 18 points below September, the best at 85.2%. 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. October was the busiest month here, with 278 flights.

Across the week, Tuesday is the strongest day at 82.0% on time and Sunday the weakest at 70.1%. 12 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. Late-arriving aircraft accounts for 46% of the 42,000 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.

Late-arriving aircraft
46%
Carrier
34%
National Airspace System
17%
Extreme weather
2%
Security
0%

46% 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 42,000 reported delay minutes here, that single category outweighs weather by 20 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 42,452 reported delay minutes.

The largest share of delay minutes, 34%, 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 14,000 of the 42,000 delay minutes reported here.

Cancellations sit at 2.12% against a national 1.81%, which is ordinary. Diversions add another 0.15%.

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. 9.2% 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.

The 632 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.

The return leg runs 74.8% on time across 2,588 flights, within 3 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.

The sample behind these figures is 2,591 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 85.2% on time and July 67.1%, a swing of 18 points. If the dates move at all, move them out of July before you think about anything else. 2,532 completed flights over 12 months sit behind that.

Common questions

BOS to DTW questions

How often is BOS to DTW delayed?

Roughly 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 22.4% of the 2,591 flights in this analysis, against 22.4% nationally. Delayed flights are late by a little over an hour on average.

Which airline is most reliable on BOS to DTW?

Delta Air Lines leads at 79.6% on time across 1,712 flights. JetBlue Airways is at the other end on 71.7%, 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 BOS to DTW?

The 5am–8am departure window is the strongest at 93.2% on time. The 8pm–5am window is the weakest at 56.1%, 37 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 BOS to DTW?

July is the weakest month at 67.1% on time, compared with 85.2% in September. Across the year that is 18 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. BOS to DTW and DTW to BOS 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