Flight number record

UA 2400

United Airlines · Boston to San Francisco

Route: BOS → SFO
Departs: 18:18
Flights: 321
Period: July 2025 to June 2026

Historical statistics for July 2025 to June 2026, not live status. For today’s UA 2400, check with United Airlines.

UA 2400 draws a D. Roughly one flight in two arrives at least 15 minutes late, and the typical late arrival is a little over an hour behind schedule. Build slack into anything you connect to. That rests on 321 flights, with a median arrival 8 minutes late.

The national on-time rate over the same period is 77.6%, so UA 2400 runs 19 points behind the country as a whole. Across a thousand flights that is about 192 extra late arrivals.

On time

58.4%

Arrivals under 15 minutes late, of 317 completed flights

Avg delay

75 min

Across delayed arrivals only, not all flights

Cancelled

1.25%

National rate is 1.81%

1 hour+ late

19.9%

National rate is 8.1%

These figures cover 321 flights between July 2025 and June 2026. Beyond the headline rate, 19.9% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.

Schedule

When UA 2400 flies

UA 2400 flies BOS to SFO without a single fixed slot. Its most common scheduled departure was 18:18, used on 68 of 321 flights, with 18:01 (52 flights) and 17:57 (51 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.

Departs 18:1868 flights21.2%
Departs 18:0152 flights16.2%
Departs 17:5751 flights15.9%

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 18:18 departure sits in the 5pm–8pm window. Across every US flight scheduled in that window the on-time rate is 68.2%, and UA 2400 runs 10 points worse at 58.4%. By that time of day most aircraft have flown several legs already, and whatever went wrong earlier is still in the schedule.

Against the route

UA 2400 next to BOS to SFO

Every carrier on BOS to SFO combined arrived on time 72.6% of the time across 4,676 flights, so UA 2400 is 14 points behind it. United flew 1,867 flights on the same city pair under all its flight numbers, including this one, and those ran 76.3% on time. Across its whole network United Airlines managed 79.0%, which this flight trails by 21 points.

UA 2400 against its route and carrier
Compared with	Flights	On time	Avg delay	Cancelled	Grade
UA 2400thin sample	321	58.4%	75 min	1.25%	D
All United Airlines on BOS–SFO	1,867	76.3%	66 min	1.12%	B
All carriers on BOS–SFO	4,676	72.6%	65 min	1.22%	C
United Airlines, whole network	821,041	79.0%	72 min	1.01%	B

Across the year

UA 2400 quarter by quarter

UA 2400 did not run the same all year. Its best quarter was Jul–Sep 2025 at 65.9% on time and its weakest Apr–Jun 2026 at 44.9%, a swing of 21 points on roughly 80 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 202591 flights65.9%
Oct–Dec 202588 flights60.9%
Jan–Mar 202652 flights64.0%
Apr–Jun 202690 flights44.9%

Scale runs 35% to 70%. Rows with fewer than 30 flights show a dash.

By weekday, UA 2400 did best on Saturday at 73.9% on time and worst on Thursday at 44.4%. Each day rests on about 46 flights, so a gap of 30 points is worth noticing but could still narrow in another year.

Delay causes

Why UA 2400 runs late

One category carries most of the weight here. National Airspace System accounts for 47% of the 9,933 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
47%
Late-arriving aircraft
36%
Carrier
17%
Extreme weather
0%

36% 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 9,933 reported delay minutes here, that single category outweighs weather by 36 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 9,933 delay minutes reported on UA 2400.

Cancellations sit at 1.25% against a national 1.81%, which is ordinary. Diversions add another 0.00%.

Connections and routes

What a delay on this flight costs

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 19.9% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.

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.

The same number turns up on four other city pairs in the data, including SFO to LAS (129), SFO to SEA (30) and IAH to BOS (21), but none flew often enough under UA 2400 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to BOS to SFO only.

One caution: this is a thin sample. 321 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 UA 2400

For a booking, UA 2400 is a flight to put a long connection behind. 19.9% of its completed flights arrived an hour or more late, which a short layover will not absorb. If the onward flight is on a separate ticket, the risk sits with you.

Where to go next

A flight number here means United Airlines’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