The definitions of Quarters is different at many other places.
Q1 - April, May, and June
Q2 - July, August, and September
Q3 - October, November, December
Q4 - January, February, and March
I always go by the one you posted araknyd but some people use this one as well. I think they do this one by "season"
as january/feb/march is still considered like winter, aka the end of the cycle. while spring is the start.