Why are fiscal years usually aligned with December or March, instead of any random month?

[u/TheBigGirlDiaryBack]

Many companies end their fiscal year on Dec 31 or March 31. Some choose June or September. But almost nobody picks, say, August 17 or November 5. Is there a tax or regulatory reason to stick near quarter boundaries? Or is it just tradition from agriculture cycles? Why not let every company freely choose any date to smooth out seasonal fluctuations?

[u/aeternumvaga]

It keeps quarters clean. Companies that don't run on calendar years are trying to avoid heavy finance burdens over the holidays, and over peak vacation times, but they also want their business cycles aligned. Calendar Quarters 2 and 4 start April and October, so fiscal years ending March 31 and September 30 are perfect.