In general, when booking your flight to Boston, February is the cheapest month on average.
On average, from most locations, when planning your trip to Boston, try to book your flight in the region of 53 days in advance for the cheapest prices.
In general, booking your departure to Boston for a Tuesday represents the best deal on airfare. Try to avoid a Sunday departure to stay away from the highest prices.
On average you can find the best deals on plane tickets to Boston when looking for flights with midday departure times.