Flight number record
DL 657
Delta Air Lines · Salt Lake City to Boston
- Route
- SLC → BOS
- Departs
- 09:35
- Flights
- 365
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 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 77.3%. About one flight in five arrives 15 minutes late or worse, and those flights are late by roughly 55 minutes on average. That rests on 365 flights, with a median arrival 6 minutes early.
Key figures
On time
81.2%
Arrivals under 15 minutes late, of 361 completed flights
Avg delay
54 min
Across delayed arrivals only, not all flights
Cancelled
1.10%
National rate is 1.89%
1 hour+ late
5.8%
National rate is 8.3%
These figures cover 365 flights between September 2025 and August 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.
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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 09:50 (56 flights) and 09:49 (38 flights) next.
- Departs 09:3557 flights15.6%
- Departs 09:5056 flights15.3%
- Departs 09:4938 flights10.4%
Scale runs 0% to 100%.
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 83.9%, and DL 657 runs 3 points worse at 81.2%. Early departures usually start with an aircraft that has not flown yet that day, which is most of why the window does well.
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Against the route
DL 657 next to SLC to BOS
Every carrier on SLC to BOS combined arrived on time 80.6% of the time across 1,264 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 82.7% on time. Across its whole network Delta Air Lines managed 81.1%, close to this flight's figure.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| DL 657 | 365 | 81.2% | 54 min | 1.10% | B |
| All Delta Air Lines on SLC–BOS | 1,083 | 82.7% | 59 min | 1.29% | B |
| All carriers on SLC–BOS | 1,264 | 80.6% | 62 min | 1.98% | B |
| Delta Air Lines, whole network | 1,039,517 | 81.1% | 71 min | 1.74% | 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 Jul–Sep 2025 at 60.0%, a swing of 28 points on roughly 73 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 202530 flights60.0%
- Oct–Dec 202592 flights75.0%
- Jan–Mar 202690 flights88.4%
- Apr–Jun 202691 flights83.5%
- Jul–Sep 202662 flights87.1%
Scale runs 50% to 95%.
By weekday, DL 657 ranged from 78.8% on Saturday 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.
Arrival by arrival
How late DL 657 runs when it is late
DL 657 often beats the schedule: 125 of 361 completed flights, 35%, arrived 15 minutes or more early. The 68 late arrivals split 24 under half an hour, 23 between 30 and 60 minutes, and 21 an hour or more.
- 15+ min early125 flights34.6%
- Within 15 min168 flights46.5%
- 15–29 min late24 flights6.6%
- 30–59 min late23 flights6.4%
- 1–2 hours late17 flights4.7%
- 2+ hours late4 flights1.1%
Scale runs 0% to 100%.
Share of 361 completed flights by arrival against schedule.
19 of 67 late departures made up the time and arrived on time, 28% of them. In the other direction, 20 flights left on time yet arrived 15 minutes late or more, so that delay built up after pushback: in the air, in a holding pattern or on the ground at BOS.
The worst days
Worst days for DL 657
The latest arrival of the period was on 24 September 2025, 4 hours 15 minutes behind schedule; most of its delay minutes were filed as national airspace system delay. The same cause led on four of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 24 September 2025 | 4 hours 15 minutes | National Airspace System |
| 16 January 2026 | 3 hours 58 minutes | Carrier |
| 14 October 2025 | 3 hours 30 minutes | National Airspace System |
| 25 September 2025 | 2 hours 54 minutes | National Airspace System |
| 8 October 2025 | 1 hour 58 minutes | National Airspace System |
Delay causes
Why DL 657 runs late
National Airspace System accounts for 66% of the 3,665 delay minutes carriers reported here, and the remaining four split what is left.
- 66%National Airspace System
- 26%Carrier
- 7%Late-arriving aircraft
- 1%Extreme weather
66% 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 2,431 minutes out of 3,665, against a national NAS share of 21%. The split is drawn from 3,665 delay minutes reported on DL 657.
Cancellations sit at 1.10% against a national 1.89%, which is ordinary. Diversions add another 0.00%.
Connections and routes
What a delay on this flight costs
5.8% of arrivals land an hour or more late, close to the national 8.3%, so 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 81.2% on time with 1.10% cancelled over 365 flights. Those are rates from the past twelve months, not a forecast for any particular day.
Related
Where to go next
- SLC to BOS, every carrier and departure
- BOS to SLC, the return direction
- Delta Air Lines 702 on the same route76.3%
- Delta Air Lines 696 on the same route91.2%
- Salt Lake City International (SLC) delay statistics
- Boston Logan International (BOS) delay statistics
- Delta Air Lines on-time record
- Every Delta Air Lines flight number with a record
- The most and least reliable flight numbers in the US
- Worst months to fly in the US, ranked by the data
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, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.