Flight number record
DL 1221
Delta Air Lines · Milwaukee to Atlanta
- Route
- MKE → ATL
- Departs
- 05:45
- Flights
- 365
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 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 77.3%. When something does go wrong the average delay runs about 2.6 hours. That rests on 365 flights, with a median arrival 15 minutes early.
Set against the rest of the country, DL 1221's record is 13 points better than the US average of 77.3%. That gap is worth roughly 132 fewer late arrivals for every thousand flights.
Key figures
On time
90.5%
Arrivals under 15 minutes late, of 359 completed flights
Avg delay
159 min
Across delayed arrivals only, not all flights
Cancelled
1.37%
National rate is 1.89%
1 hour+ late
4.5%
National rate is 8.3%
These figures cover 365 flights between September 2025 and August 2026. The median arrival is 15 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 DL 1221 flies
DL 1221 flies MKE to ATL without a single fixed slot. Its most common scheduled departure was 05:45, used on 96 of 365 flights, with 05:40 (76 flights) and 05:30 (63 flights) next.
- Departs 05:4596 flights26.3%
- Departs 05:4076 flights20.8%
- Departs 05:3063 flights17.3%
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 05:45 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 90.5%. 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
DL 1221 next to MKE to ATL
Every carrier on MKE to ATL combined arrived on time 88.5% of the time across 2,264 flights, so DL 1221 is 2 points ahead of it. Delta flew 2,202 flights on the same city pair under all its flight numbers, including this one, and those ran 89.1% on time. Across its whole network Delta Air Lines managed 81.1%, which this flight beats by 9 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| DL 1221 | 365 | 90.5% | 159 min | 1.37% | A |
| All Delta Air Lines on MKE–ATL | 2,202 | 89.1% | 89 min | 2.00% | A |
| All carriers on MKE–ATL | 2,264 | 88.5% | 86 min | 1.99% | A |
| Delta Air Lines, whole network | 1,039,517 | 81.1% | 71 min | 1.74% | B |
Across the year
DL 1221 quarter by quarter
DL 1221 did not run the same all year. Its best quarter was Jul–Sep 2025 at 100.0% on time and its weakest Jan–Mar 2026 at 86.5%, a swing of 14 points on roughly 73 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 flights100.0%
- Oct–Dec 202592 flights87.6%
- Jan–Mar 202690 flights86.5%
- Apr–Jun 202691 flights91.1%
- Jul–Sep 202662 flights95.1%
Scale runs 80% to 100%.
By weekday, DL 1221 ranged from 88.0% on Sunday to 94.2% on Thursday. With about 52 flights behind each day, a spread of 6 points is inside normal variation, so the day you fly is not worth changing for this flight.
Arrival by arrival
How late DL 1221 runs when it is late
DL 1221 often beats the schedule: 184 of 359 completed flights, 51%, arrived 15 minutes or more early. The 34 late arrivals split 11 under half an hour, 7 between 30 and 60 minutes, and 16 an hour or more.
- 15+ min early184 flights51.3%
- Within 15 min141 flights39.3%
- 15–29 min late11 flights3.1%
- 30–59 min late7 flights1.9%
- 1–2 hours late2 flights0.6%
- 2+ hours late14 flights3.9%
Scale runs 0% to 100%.
Share of 359 completed flights by arrival against schedule.
Time lost at the gate mostly stays lost. Of 22 departures that left 15 minutes late or more, only 2 made it up before arrival. 14 flights left on time and still arrived late.
The worst days
Worst days for DL 1221
The latest arrival of the period was on 7 January 2026, 16 hours 9 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The same cause led on four of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 7 January 2026 | 16 hours 9 minutes | Carrier |
| 15 January 2026 | 10 hours 23 minutes | Carrier |
| 10 December 2025 | 8 hours 2 minutes | Carrier |
| 7 December 2025 | 7 hours 17 minutes | National Airspace System |
| 31 August 2026 | 6 hours 44 minutes | Carrier |
Delay causes
Why DL 1221 runs late
Carrier accounts for 71% of the 5,401 delay minutes carriers reported here, and the remaining four split what is left.
- 71%Carrier
- 16%National Airspace System
- 12%Late-arriving aircraft
- 1%Extreme weather
The largest share of delay minutes, 71%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 3,855 of the 5,401 delay minutes reported here. The split is drawn from 5,401 delay minutes reported on DL 1221.
Cancellations sit at 1.37% against a national 1.89%, 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 8.3% 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.
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.
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: 90.5% on time and 1.37% cancelled. That is a base rate, not a promise about any single day.
Related
Where to go next
- MKE to ATL, every carrier and departure
- ATL to MKE, the return direction
- Delta Air Lines 1236 on the same route89.4%
- Delta Air Lines 2999 on the same route95.1%
- Delta Air Lines 1151 on the same route90.0%
- Delta Air Lines 2152 on the same route86.7%
- Delta Air Lines 1246 on the same route85.2%
- Milwaukee Mitchell International (MKE) delay statistics
- Hartsfield-Jackson Atlanta International (ATL) delay statistics
- Delta Air Lines on-time record
- Every Delta Air Lines flight number with a record
- The most and least reliable flight numbers in the US
- Worst months to fly in the US, ranked by the data
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, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.