Flight number record

DL 1221

Delta Air Lines · Milwaukee to Atlanta

Route: MKE → ATL
Departs: 05:40
Flights: 365
Period: July 2025 to June 2026

Historical statistics for July 2025 to June 2026, not live status. For today’s DL 1221, check with Delta Air Lines.

DL 1221 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 13 points better than the national rate of 77.6%. When something does go wrong the average delay runs about 2.5 hours. That rests on 365 flights, with a median arrival 16 minutes early.

Set against the rest of the country, DL 1221's record is 13 points better than the US average of 77.6%. That gap is worth roughly 127 fewer late arrivals for every thousand flights.

On time

90.3%

Arrivals under 15 minutes late, of 359 completed flights

Avg delay

148 min

Across delayed arrivals only, not all flights

Cancelled

1.37%

National rate is 1.81%

1 hour+ late

4.5%

National rate is 8.1%

These figures cover 365 flights between July 2025 and June 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.

Schedule

When DL 1221 flies

DL 1221 flies MKE to ATL without a single fixed slot. Its most common scheduled departure was 05:40, used on 97 of 365 flights, with 05:45 (77 flights) and 05:30 (63 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.

Departs 05:4097 flights26.6%
Departs 05:4577 flights21.1%
Departs 05:3063 flights17.3%

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 05:40 departure sits in the 5am–8am window. Across every US flight scheduled in that window the on-time rate is 89.3%, and DL 1221 runs level with that at 90.3%. 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 1221 next to MKE to ATL

Every carrier on MKE to ATL combined arrived on time 89.4% of the time across 2,267 flights, so DL 1221 is about level with it. Delta flew 2,205 flights on the same city pair under all its flight numbers, including this one, and those ran 90.0% on time. Across its whole network Delta Air Lines managed 81.6%, which this flight beats by 9 points.

DL 1221 against its route and carrier
Compared with	Flights	On time	Avg delay	Cancelled	Grade
DL 1221	365	90.3%	148 min	1.37%	A
All Delta Air Lines on MKE–ATL	2,205	90.0%	96 min	1.90%	A
All carriers on MKE–ATL	2,267	89.4%	92 min	1.90%	A
Delta Air Lines, whole network	1,038,570	81.6%	71 min	1.62%	B

Across the year

DL 1221 quarter by quarter

Quarter by quarter DL 1221 held fairly steady: 95.6% in Jul–Sep 2025, 87.6% in Oct–Dec 2025, 86.5% 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 flights95.6%
Oct–Dec 202592 flights87.6%
Jan–Mar 202690 flights86.5%
Apr–Jun 202691 flights91.1%

Scale runs 80% to 100%. Rows with fewer than 30 flights show a dash.

By weekday, DL 1221 ranged from 86.3% on Sunday to 94.2% on Thursday. With about 52 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.

Delay causes

Why DL 1221 runs late

One category carries most of the weight here. Carrier accounts for 65% of the 5,181 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
65%
National Airspace System
17%
Late-arriving aircraft
12%
Extreme weather
6%

The largest share of delay minutes, 65%, 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 3,362 of the 5,181 delay minutes reported here. The split is drawn from 5,181 delay minutes reported on DL 1221.

Cancellations sit at 1.37% 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 4.5% 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.

The 669 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 365 flights under DL 1221 in the data flew MKE to ATL. 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. 365 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 1221

For a booking, DL 1221 has one of the better records a US domestic flight can show: 90.3% on time and 1.37% cancelled. That is a base rate, not a promise about any single 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