Flight number record

DL 657

Delta Air Lines · Salt Lake City to Boston

Route: SLC → BOS
Departs: 09:35
Flights: 365
Period: July 2025 to June 2026

Historical statistics for July 2025 to June 2026, not live status. For today’s DL 657, check with Delta Air Lines.

DL 657 lands a B, 4 points better than the national rate of 77.6%. Roughly one flight in five arrives 15 minutes late or worse, and those flights are late by roughly 55 minutes on average. That is a workable record, not a spotless one. That rests on 365 flights, with a median arrival 8 minutes early.

Set against the rest of the country, DL 657's record is 4 points better than the US average of 77.6%. That gap is worth roughly 41 fewer late arrivals for every thousand flights.

On time

81.7%

Arrivals under 15 minutes late, of 361 completed flights

Avg delay

53 min

Across delayed arrivals only, not all flights

Cancelled

1.10%

National rate is 1.81%

1 hour+ late

5.3%

National rate is 8.1%

These figures cover 365 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.

Schedule

When DL 657 flies

DL 657 flies SLC to BOS without a single fixed slot. Its most common scheduled departure was 09:35, used on 57 of 365 flights, with 09:45 (41 flights) and 09:49 (38 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.

Departs 09:3557 flights15.6%
Departs 09:4541 flights11.2%
Departs 09:4938 flights10.4%

Scale runs 0% to 100%. Rows with fewer than 30 flights show a dash.

Share of scheduled departures at each local time. Times used on fewer than one flight in ten are not listed.

A 09:35 departure sits in the 8am–11am window. Across every US flight scheduled in that window the on-time rate is 84.1%, and DL 657 runs 2 points worse at 81.7%. Early departures usually start with an aircraft that has not flown yet that day, which is most of why the window does well.

Against the route

DL 657 next to SLC to BOS

Every carrier on SLC to BOS combined arrived on time 82.2% of the time across 1,256 flights, so DL 657 is about level with it. Delta flew 1,083 flights on the same city pair under all its flight numbers, including this one, and those ran 83.3% on time. Across its whole network Delta Air Lines managed 81.6%, close to this flight's figure.

DL 657 against its route and carrier
Compared with	Flights	On time	Avg delay	Cancelled	Grade
DL 657	365	81.7%	53 min	1.10%	B
All Delta Air Lines on SLC–BOS	1,083	83.3%	60 min	1.29%	B
All carriers on SLC–BOS	1,256	82.2%	61 min	1.75%	B
Delta Air Lines, whole network	1,038,570	81.6%	71 min	1.62%	B

Across the year

DL 657 quarter by quarter

DL 657 did not run the same all year. Its best quarter was Jan–Mar 2026 at 88.4% on time and its weakest Oct–Dec 2025 at 75.0%, a swing of 13 points on roughly 91 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.

Jul–Sep 202592 flights80.4%
Oct–Dec 202592 flights75.0%
Jan–Mar 202690 flights88.4%
Apr–Jun 202691 flights83.5%

Scale runs 65% to 95%. Rows with fewer than 30 flights show a dash.

By weekday, DL 657 ranged from 78.8% on Friday to 84.6% on Wednesday. With about 52 flights behind each day, a spread of 6 points is inside normal variation, so the day you fly is not worth changing for this flight.

Delay causes

Why DL 657 runs late

One category carries most of the weight here. National Airspace System accounts for 63% of the 3,497 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.

National Airspace System
63%
Carrier
27%
Late-arriving aircraft
9%

63% 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 2,209 minutes out of 3,497, against a national NAS share of 21%. The split is drawn from 3,497 delay minutes reported on DL 657.

Cancellations sit at 1.10% against a national 1.81%, which is ordinary. Diversions add another 0.00%.

Connections and routes

What a delay on this flight costs

5.3% 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 roughly 55 minutes, which a normal layover absorbs.

At 2,105 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.

Every one of the 365 flights under DL 657 in the data flew SLC to BOS. The number was not reused on any other city pair, which makes this a clean record of one route.

One caution: this is a thin sample. 365 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.

What to do with this

Booking DL 657

For a booking, read DL 657 as 81.7% on time with 1.10% cancelled over 365 flights. Those are rates from the past twelve months, not a forecast for any particular day.

Where to go next

A flight number here means Delta Air Lines’s own number as it reports to the DOT. How the figures are computed is on the methodology page.

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.

Key figures