Flight number record

DL 400

Delta Air Lines · San Francisco to Boston

Route: SFO → BOS
Departs: 07:05
Flights: 364
Period: July 2025 to June 2026

Historical statistics for July 2025 to June 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 12 points better than the national rate of 77.6%. When something does go wrong the average delay runs an hour and a half. That rests on 364 flights, with a median arrival 11 minutes early.

Set against the rest of the country, DL 400's record is 12 points better than the US average of 77.6%. That gap is worth roughly 115 fewer late arrivals for every thousand flights.

On time

89.1%

Arrivals under 15 minutes late, of 357 completed flights

Avg delay

85 min

Across delayed arrivals only, not all flights

Cancelled

1.65%

National rate is 1.81%

1 hour+ late

3.1%

National rate is 8.1%

These figures cover 364 flights between July 2025 and June 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.

Schedule

When DL 400 flies

DL 400 flies SFO to BOS without a single fixed slot. Its most common scheduled departure was 07:05, used on 111 of 364 flights, with 07:00 (108 flights) and 07:10 (92 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.

Departs 07:05111 flights30.5%
Departs 07:00108 flights29.7%
Departs 07:1092 flights25.3%

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 07:05 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 89.1%. 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 400 next to SFO to BOS

Every carrier on SFO to BOS combined arrived on time 76.9% of the time across 4,674 flights, so DL 400 is 12 points ahead of it. Delta flew 899 flights on the same city pair under all its flight numbers, including this one, and those ran 75.1% on time. Across its whole network Delta Air Lines managed 81.6%, which this flight beats by 8 points.

DL 400 against its route and carrier
Compared with	Flights	On time	Avg delay	Cancelled	Grade
DL 400thin sample	364	89.1%	85 min	1.65%	A
All Delta Air Lines on SFO–BOS	899	75.1%	73 min	1.45%	B
All carriers on SFO–BOS	4,674	76.9%	74 min	1.35%	B
Delta Air Lines, whole network	1,038,570	81.6%	71 min	1.62%	B

Across the year

DL 400 quarter by quarter

Quarter by quarter DL 400 held fairly steady: 85.9% in Jul–Sep 2025, 85.4% in Oct–Dec 2025, 94.2% in Jan–Mar 2026 and 91.1% in Apr–Jun 2026. A spread of 9 points is about what a sample of this size moves on its own, so the annual figure is a fair summary.

Jul–Sep 202592 flights85.9%
Oct–Dec 202591 flights85.4%
Jan–Mar 202690 flights94.2%
Apr–Jun 202691 flights91.1%

Scale runs 75% to 100%. Rows with fewer than 30 flights show a dash.

By weekday, DL 400 ranged from 84.6% on Wednesday to 94.1% on Friday. With about 52 flights behind each day, a spread of 10 points is inside normal variation, so the day you fly is not worth changing for this flight.

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 3,299 reported delay minutes.

National Airspace System
39%
Late-arriving aircraft
39%
Carrier
23%

39% 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 3,299 reported delay minutes here, that single category outweighs weather by 39 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 3,299 delay minutes reported on DL 400.

Cancellations sit at 1.65% 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 3.1% 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 2,704 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 89.1% on time with 1.65% 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, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.

Key figures