Flight number record

DL 400

Delta Air Lines · San Francisco to Boston

Route: SFO → BOS
Departs: 07:10
Flights: 364
Period: September 2025 to August 2026

Historical statistics for September 2025 to August 2026, not live status. For today’s DL 400, check with Delta Air Lines.

DL 400 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 11 points better than the national rate of 77.3%. When something does go wrong the average delay runs a little over an hour. That rests on 364 flights, with a median arrival 11 minutes early.

Set against the rest of the country, DL 400's record is 11 points better than the US average of 77.3%. That gap is worth roughly 112 fewer late arrivals for every thousand flights.

On time

88.5%

Arrivals under 15 minutes late, of 356 completed flights

Avg delay

82 min

Across delayed arrivals only, not all flights

Cancelled

1.92%

National rate is 1.89%

1 hour+ late

3.1%

National rate is 8.3%

These figures cover 364 flights between September 2025 and August 2026. The median arrival is 11 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 400 flies

DL 400 flies SFO to BOS without a single fixed slot. Its most common scheduled departure was 07:10, used on 119 of 364 flights, with 07:00 (102 flights) and 07:05 (90 flights) next.

Departs 07:10119 flights32.7%
Departs 07:00102 flights28.0%
Departs 07:0590 flights24.7%

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 07:10 departure sits in the 5am–8am window. Across every US flight scheduled in that window the on-time rate is 89.3%, and DL 400 runs level with that at 88.5%. 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 400 next to SFO to BOS

Every carrier on SFO to BOS combined arrived on time 74.5% of the time across 4,815 flights, so DL 400 is 14 points ahead of it. Delta flew 946 flights on the same city pair under all its flight numbers, including this one, and those ran 71.5% on time. Across its whole network Delta Air Lines managed 81.1%, which this flight beats by 7 points.

DL 400 against its route and carrier
Compared with	Flights	On time	Avg delay	Cancelled	Grade
DL 400thin sample	364	88.5%	82 min	1.92%	A
All Delta Air Lines on SFO–BOS	946	71.5%	69 min	1.59%	C
All carriers on SFO–BOS	4,815	74.5%	74 min	1.81%	C
Delta Air Lines, whole network	1,039,517	81.1%	71 min	1.74%	B

Across the year

DL 400 quarter by quarter

DL 400 did not run the same all year. Its best quarter was Jan–Mar 2026 at 94.2% on time and its weakest Jul–Sep 2025 at 70.0%, a swing of 24 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 flights70.0%
Oct–Dec 202591 flights85.4%
Jan–Mar 202690 flights94.2%
Apr–Jun 202691 flights91.1%
Jul–Sep 202662 flights90.2%

Scale runs 60% to 100%.

By weekday, DL 400 ranged from 86.0% on Saturday to 92.2% on Friday. 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 400 runs when it is late

DL 400 often beats the schedule: 138 of 356 completed flights, 39%, arrived 15 minutes or more early. Most of the lateness is short. 21 of the 41 late arrivals were under half an hour behind, and 11 reached an hour or more.

15+ min early138 flights38.8%
Within 15 min177 flights49.7%
15–29 min late21 flights5.9%
30–59 min late9 flights2.5%
1–2 hours late4 flights1.1%
2+ hours late7 flights2.0%

Scale runs 0% to 100%.

Share of 356 completed flights by arrival against schedule.

Time lost at the gate mostly stays lost. Of 21 departures that left 15 minutes late or more, only 2 made it up before arrival. In the other direction, 22 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 400

The latest arrival of the period was on 15 January 2026, 9 hours 29 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. The same cause led on three of the five worst days.

The latest arrivals of DL 400 in the period
Date	Arrived late by	Largest filed cause
15 January 2026	9 hours 29 minutes	Late-arriving aircraft
15 October 2025	6 hours 53 minutes	Late-arriving aircraft
30 May 2026	5 hours 56 minutes	Carrier
26 September 2025	5 hours 11 minutes	Late-arriving aircraft
14 October 2025	3 hours 54 minutes	National Airspace System

Delay causes

Why DL 400 runs late

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 3,357 reported delay minutes.

National Airspace System
40%
Late-arriving aircraft
38%
Carrier
22%

38% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 3,357 reported delay minutes here, that single category outweighs weather by 38 to one. The split is drawn from 3,357 delay minutes reported on DL 400.

Cancellations sit at 1.92% against a national 1.89%, 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 3.1% land an hour or more behind schedule, against 8.3% 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 2,704 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 364 flights under DL 400 in the data flew SFO 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. 364 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 400

For a booking, read DL 400 as 88.5% on time with 1.92% cancelled over 364 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, September 2025 to August 2026. Last updated 22 October 2026; recomputed monthly. How this data is collected.

Key figures