We do not have enough data on this route to provide a reliable graph showing how many days before departure it is the best to book.
However, usually the closer it is to the departure, the more expensive the tickets are.
The most popular airlines on the route Washington Dulles - Boston Edward L. Logan: United Airlines (UA), JetBlue (B6).
Direct flights last about 1h 26min.
Direct flights available 3 days a week - Wednesday, Thursday, Sunday.
Direct flights: United Airlines (UA), JetBlue (B6).
Washington (DC) Boston (MA)