Flight number record

DL 859

Delta Air Lines · Boston to Salt Lake City

Route: BOS → SLC
Departs: 06:10
Flights: 365
Period: July 2025 to June 2026

Historical statistics for July 2025 to June 2026, not live status. For today’s DL 859, check with Delta Air Lines.

DL 859 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 roughly 45 minutes. That rests on 365 flights, with a median arrival 8 minutes early.

Set against the rest of the country, DL 859's record is 10 points better than the US average of 77.6%. That gap is worth roughly 101 fewer late arrivals for every thousand flights.

On time

87.7%

Arrivals under 15 minutes late, of 358 completed flights

Avg delay

43 min

Across delayed arrivals only, not all flights

Cancelled

1.64%

National rate is 1.81%

1 hour+ late

2.2%

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 859 flies

DL 859 flies BOS to SLC without a single fixed slot. Its most common scheduled departure was 06:10, used on 205 of 365 flights, with 06:15 (92 flights) and 06:00 (41 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.

Departs 06:10205 flights56.2%
Departs 06:1592 flights25.2%
Departs 06:0041 flights11.2%

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 06:10 departure sits in the 5am–8am window. Across every US flight scheduled in that window the on-time rate is 89.3%, and DL 859 runs level with that at 87.7%. 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 859 next to BOS to SLC

Every carrier on BOS to SLC combined arrived on time 75.4% of the time across 1,256 flights, so DL 859 is 12 points ahead of it. Delta flew 1,083 flights on the same city pair under all its flight numbers, including this one, and those ran 77.8% on time. Across its whole network Delta Air Lines managed 81.6%, which this flight beats by 6 points.

DL 859 against its route and carrier
Compared with	Flights	On time	Avg delay	Cancelled	Grade
DL 859	365	87.7%	43 min	1.64%	A
All Delta Air Lines on BOS–SLC	1,083	77.8%	68 min	1.20%	B
All carriers on BOS–SLC	1,256	75.4%	65 min	1.51%	B
Delta Air Lines, whole network	1,038,570	81.6%	71 min	1.62%	B

Across the year

DL 859 quarter by quarter

DL 859 did not run the same all year. Its best quarter was Jul–Sep 2025 at 97.8% on time and its weakest Jan–Mar 2026 at 80.0%, a swing of 18 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 flights97.8%
Oct–Dec 202592 flights85.9%
Jan–Mar 202690 flights80.0%
Apr–Jun 202691 flights86.7%

Scale runs 70% to 100%. Rows with fewer than 30 flights show a dash.

By weekday, DL 859 did best on Monday at 92.0% on time and worst on Saturday at 78.8%. Each day rests on about 52 flights, so a gap of 13 points is worth noticing but could still narrow in another year.

Delay causes

Why DL 859 runs late

One category carries most of the weight here. Carrier accounts for 55% of the 1,900 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.

Carrier
55%
National Airspace System
45%
Extreme weather
0%

45% 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 853 minutes out of 1,900, against a national NAS share of 21%. The split is drawn from 1,900 delay minutes reported on DL 859.

Cancellations sit at 1.64% against a national 1.81%, which is ordinary. Diversions add another 0.27%.

Connections and routes

What a delay on this flight costs

Badly late arrivals are rare here: only 2.2% 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 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 859 in the data flew BOS to SLC. 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 859

For a booking, read DL 859 as 87.7% on time with 1.64% 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