Flight number record

DL 1633

Delta Air Lines · Detroit to Houston

Route: DTW → IAH
Departs: 20:15
Flights: 364
Period: July 2025 to June 2026

Historical statistics for July 2025 to June 2026, not live status. For today’s DL 1633, check with Delta Air Lines.

DL 1633 lands a B, 2 points better than the national rate of 77.6%. About one flight in five arrives 15 minutes late or worse, and those flights are late by about an hour on average. That is a workable record, not a spotless one. That rests on 364 flights, with a median arrival 5 minutes early.

On time

79.1%

Arrivals under 15 minutes late, of 359 completed flights

Avg delay

62 min

Across delayed arrivals only, not all flights

Cancelled

1.10%

National rate is 1.81%

1 hour+ late

7.0%

National rate is 8.1%

These figures cover 364 flights between July 2025 and June 2026. The median arrival is 5 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 1633 flies

DL 1633 flies DTW to IAH without a single fixed slot. Its most common scheduled departure was 20:15, used on 101 of 364 flights, with 20:48 (60 flights) and 19:55 (52 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.

Departs 20:15101 flights27.7%
Departs 20:4860 flights16.5%
Departs 19:5552 flights14.3%

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 20:15 departure sits in the 8pm–5am window. Across every US flight scheduled in that window the on-time rate is 70.5%, and DL 1633 runs 9 points better at 79.1%. 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

DL 1633 next to DTW to IAH

Every carrier on DTW to IAH combined arrived on time 79.7% of the time across 2,129 flights, so DL 1633 is about level with it. Delta flew 1,322 flights on the same city pair under all its flight numbers, including this one, and those ran 79.8% on time. Across its whole network Delta Air Lines managed 81.6%, which this flight trails by 3 points.

DL 1633 against its route and carrier
Compared with	Flights	On time	Avg delay	Cancelled	Grade
DL 1633thin sample	364	79.1%	62 min	1.10%	B
All Delta Air Lines on DTW–IAH	1,322	79.8%	55 min	0.83%	B+
All carriers on DTW–IAH	2,129	79.7%	63 min	1.08%	B
Delta Air Lines, whole network	1,038,570	81.6%	71 min	1.62%	B

Across the year

DL 1633 quarter by quarter

Quarter by quarter DL 1633 held fairly steady: 78.0% in Jul–Sep 2025, 77.8% in Oct–Dec 2025, 82.8% in Jan–Mar 2026 and 78.0% in Apr–Jun 2026. A spread of 5 points is about what a sample of this size moves on its own, so the annual figure is a fair summary.

Jul–Sep 202592 flights78.0%
Oct–Dec 202591 flights77.8%
Jan–Mar 202690 flights82.8%
Apr–Jun 202691 flights78.0%

Scale runs 70% to 90%. Rows with fewer than 30 flights show a dash.

By weekday, DL 1633 did best on Wednesday at 86.5% on time and worst on Thursday at 74.5%. Each day rests on about 52 flights, so a gap of 12 points is worth noticing but could still narrow in another year.

Delay causes

Why DL 1633 runs late

One category carries most of the weight here. Carrier accounts for 64% of the 4,609 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
64%
National Airspace System
18%
Late-arriving aircraft
16%
Extreme weather
2%

The largest share of delay minutes, 64%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 2,939 of the 4,609 delay minutes reported here. The split is drawn from 4,609 delay minutes reported on DL 1633.

Cancellations sit at 1.10% against a national 1.81%, which is ordinary. Diversions add another 0.27%.

Connections and routes

What a delay on this flight costs

7.0% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last about an hour, which a normal layover absorbs.

The 1,075 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.

Every one of the 364 flights under DL 1633 in the data flew DTW to IAH. 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 1633

For a booking, read DL 1633 as 79.1% on time with 1.10% 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