Today: DL 571 at 22:00 is the safest bet, 15% chance of being 15+ min late; morning flights run 18–33%.

Safest bet today DL 571 SAN 22:00 → BOS 06:38 · 15% chance 15+ min late · usually 85% on time Riskiest WN 4930 SAN 14:35 → BOS 23:10 · 48% chance 15+ min late · usually 35% on time

Against a calm day 30% average chance a nonstop arrives 15+ min late; 23% for the same flights on a calm-weather day

Every nonstop today

12-month record →

Ranked by the chance of arriving 15+ minutes late, with each flight’s on-time record over Aug 2025 – Jul 2026 beside it. Times are local. Pick a flight for its forecast. Click a column to sort.


DL 571 Delta Flight history →	SAN 22:00	BOS 06:38	15%	3%	0.9%	85%
AS 390 Alaska Flight history →	SAN 07:00	BOS 15:51	18%	7%	0.8%	76%
AS 255 Alaska Flight history →	SAN 20:52	BOS 05:40	23%	5%	0.8%	85%
B6 2120 JetBlue Flight history →	SAN 20:40	BOS 05:19	28%	12%	1.2%	83%worse than usual
AS 389 Alaska	SAN 08:15	BOS 16:34	33%	9%	0.8%	no record
WN 4675 Southwest	SAN 09:30	BOS 17:54	35%	10%	0.3%	no record
B6 220 JetBlue Flight history →	SAN 13:06	BOS 21:51	36%	19%	0.7%	74%worse than usual
B6 620 JetBlue Flight history →	SAN 10:20	BOS 19:06	37%	15%	0.6%	78%worse than usual
WN 4930 Southwest Flight history →	SAN 14:35	BOS 23:10	48%	14%	0.2%	35%

Alternatives with one stop that day

All connections →


Southwest Details →	SAN 12:10 → MDW 18:10WN 4163	1h 25m Chicago	MDW 19:35 → BOS 22:55WN 232	7h 45m	91%	69%
Southwest Details →	SAN 06:30 → DEN 09:55WN 3493	1h 05m Denver	DEN 11:00 → BOS 16:53WN 1553	7h 23m	97%	63%
United Details →	SAN 10:55 → DEN 14:27UA 1715	1h 13m Denver	DEN 15:40 → BOS 21:29UA 1912	7h 34m	95%	60%

How these are worked out. Each flight’s odds are our forecast for that day; flights of airlines we don’t forecast yet use their 12-month record and are marked. Makes the connection: the first flight’s 12-month lateness curve, scaled so its chance of arriving 15+ min late matches the day’s forecast, at the layover minus the 45-minute minimum (90 on separate tickets). Arrives on time: first flight not cancelled × connection made × second flight not cancelled × second flight within 15 minutes, each from the day’s forecast.

About this data: forecast odds from our model for Mon, Oct 5 (newest published update); 12-month records from US DOT on-time data, Aug 2025 – Jul 2026, all US airlines; regional flights count under the airline that sells them. JSON