The number of finishers at the Boston Marathon used to be consistent, plus or minus a couple of hundred runners. For the five Bostons between 2015 and 2019, the finishers ranged from 25,907 to 26,762 each year, according to the Boston Athletic Association, which puts on the event. But as demand for marathons—especially the World Marathon Majors—grew after the pandemic, the field size has spiked in the two most recent editions of the race: There were 28,409 finishers in 2025 and 29,033 in 2026.