Today: UA 1734 at 05:45 is the safest bet, 5% chance of being 15+ min late; evening flights run 20–24%.

Safest bet today UA 1734 BOS 05:45 → IAD 07:23 · 5% chance 15+ min late · usually 97% on time Riskiest UA 2136 BOS 19:27 → IAD 21:16 · 24% chance 15+ min late · usually 71% on time

Against a calm day 18% average chance a nonstop arrives 15+ min late; 14% 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.


UA 1734 United Flight history →	BOS 05:45	IAD 07:23	5%	2%	0.5%	97%
UA 2098 United Flight history →	BOS 09:25	IAD 11:07	16%	4%	0.4%	91%
UA 721 United Flight history →	BOS 14:15	IAD 15:57	18%	6%	0.6%	78%
UA 3413 United flown by Republic Flight history →	BOS 12:35	IAD 14:43	19%	9%	0.6%	85%
UA 3543 United flown by Republic Flight history →	BOS 18:05	IAD 20:20	20%	8%	0.7%	75%
YX 3409 Republic	BOS 17:56	IAD 20:17	22%	7%	0.7%	no record
UA 2136 United Flight history →	BOS 19:27	IAD 21:16	24%	10%	0.6%	71%

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