A quick Google shows 65% of public companies use calendar year as their FY.
At our startup, it's even more complicated :) we use calendar year for official financial / business metrics, while our planning quarter is offset by 1 month (Q1 = Feb/Mar/Apr).
At least you're using the actual months. I've recently had to deal with 4-5-4 Retail Calendars. Explaining to my coworkers why the data for September includes dates from both August and October, and that's Working As Intended.
At our startup, it's even more complicated :) we use calendar year for official financial / business metrics, while our planning quarter is offset by 1 month (Q1 = Feb/Mar/Apr).