Flight number record

UA 558

United Airlines · Denver to Boston

Route: DEN → BOS
Departs: 07:45
Flights: 337
Period: September 2025 to August 2026

Historical statistics for September 2025 to August 2026, not live status. For today’s UA 558, check with United Airlines.

UA 558 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 15 points better than the national rate of 77.3%. When something does go wrong the average delay runs about 50 minutes. That rests on 337 flights, with a median arrival 16 minutes early.

Set against the rest of the country, UA 558's record is 15 points better than the US average of 77.3%. That gap is worth roughly 146 fewer late arrivals for every thousand flights.

On time

91.9%

Arrivals under 15 minutes late, of 333 completed flights

Avg delay

51 min

Across delayed arrivals only, not all flights

Cancelled

0.59%

National rate is 1.89%

1 hour+ late

1.2%

National rate is 8.3%

These figures cover 337 flights between September 2025 and August 2026. The median arrival is 16 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 UA 558 flies

UA 558 flies DEN to BOS without a single fixed slot. Its most common scheduled departure was 07:45, used on 153 of 337 flights, with 08:01 (58 flights) and 08:05 (55 flights) next.

Departs 07:45153 flights45.4%
Departs 08:0158 flights17.2%
Departs 08:0555 flights16.3%

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 07:45 departure sits in the 5am–8am window. Across every US flight scheduled in that window the on-time rate is 89.3%, and UA 558 runs 3 points better at 91.9%. 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

UA 558 next to DEN to BOS

Every carrier on DEN to BOS combined arrived on time 69.6% of the time across 3,851 flights, so UA 558 is 22 points ahead of it. United flew 1,887 flights on the same city pair under all its flight numbers, including this one, and those ran 76.8% on time. Across its whole network United Airlines managed 78.8%, which this flight beats by 13 points.

UA 558 against its route and carrier
Compared with	Flights	On time	Avg delay	Cancelled	Grade
UA 558thin sample	337	91.9%	51 min	0.59%	A+
All United Airlines on DEN–BOS	1,887	76.8%	75 min	0.95%	B+
All carriers on DEN–BOS	3,851	69.6%	73 min	1.45%	C
United Airlines, whole network	830,825	78.8%	73 min	1.02%	B

Across the year

UA 558 quarter by quarter

UA 558 did not run the same all year. Its best quarter was Jul–Sep 2026 at 98.3% on time and its weakest Oct–Dec 2025 at 83.8%, a swing of 15 points on roughly 67 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 flights86.7%
Oct–Dec 202581 flights83.8%
Jan–Mar 202676 flights91.9%
Apr–Jun 202691 flights96.7%
Jul–Sep 202659 flights98.3%

Scale runs 75% to 100%.

By weekday, UA 558 ranged from 88.5% on Sunday to 96.1% on Friday. With about 48 flights behind each day, a spread of 8 points is inside normal variation, so the day you fly is not worth changing for this flight.

Arrival by arrival

How late UA 558 runs when it is late

UA 558 often beats the schedule: 174 of 333 completed flights, 52%, arrived 15 minutes or more early. The 27 late arrivals split 10 under half an hour, 13 between 30 and 60 minutes, and 4 an hour or more.

15+ min early174 flights52.3%
Within 15 min132 flights39.6%
15–29 min late10 flights3.0%
30–59 min late13 flights3.9%
1–2 hours late1 flights0.3%
2+ hours late3 flights0.9%

Scale runs 0% to 100%.

Share of 333 completed flights by arrival against schedule.

3 of 20 late departures made up the time and arrived on time, 15% of them. 10 flights left on time and still arrived late.

The worst days

Worst days for UA 558

The latest arrival of the period was on 18 September 2025, 4 hours behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The five worst days are spread across September, October and November, with no single month standing out.

The latest arrivals of UA 558 in the period
Date	Arrived late by	Largest filed cause
18 September 2025	4 hours	Carrier
14 October 2025	2 hours 26 minutes	National Airspace System
25 September 2025	2 hours 17 minutes	Late-arriving aircraft
18 November 2025	1 hour 8 minutes	Late-arriving aircraft
29 October 2025	59 minutes	National Airspace System

Delay causes

Why UA 558 runs late

National Airspace System accounts for 43% of the 1,366 delay minutes carriers reported here, and the remaining four split what is left.

National Airspace System
43%
Late-arriving aircraft
29%
Carrier
28%

43% 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 588 minutes out of 1,366, against a national NAS share of 21%. The split is drawn from 1,366 delay minutes reported on UA 558.

Cancellations are rare at 0.59%, below the national 1.89% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.

Connections and routes

What a delay on this flight costs

Badly late arrivals are rare here: only 1.2% 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 1,754 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 one other city pair in the data, including BOS to EWR (32), but none flew often enough under UA 558 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to DEN to BOS only.

One caution: this is a thin sample. 337 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 558

For a booking, UA 558 has one of the better records a US domestic flight can show: 91.9% on time and 0.59% cancelled. That is a base rate, not a promise about any single day.

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, September 2025 to August 2026. Last updated 22 October 2026; recomputed monthly. How this data is collected.

Key figures