Most of Boston’s rental homes and apartments have leases that begin on September 1st. At my firm, 74% of all rentals in the past 5 years have had a September 1st start date. This is based on a diverse sample of nearly 5000 rental transactions that occurred from 2010 to 2014. Here is more about the source and methodology behind this data.
Good statistics on this phenomenon are surprisingly hard to find. The best comparisons that I could find are a few years old: Broker Ethan Goodrich reported in 2011 that 80% of his listings are for September 1st. Listing database company RentJuice published a report in 2011 stating that 79% of their listings had move-in dates between September 1st – 14th (RentJuice was later taken over by Zillow, and they have not published any data on move in dates since then).
This percent of leases that begin on September 1st has stayed almost constant over the past 5 years, indicating that the average length of all leases, new and renewing, is 12 months. If the average length was not 12 months the percentage of September 1st move-ins would change year-over-year.