You can google accounting and income statement, you'll see why it is done at least quarterly...as a business your operation occurs over a period of time, as suc

You can google accounting and income statement, you'll see why it is done at least quarterly...as a business your operation occurs over a period of time, as such the impact on your books need to be updated accordingly...it is not just a matter of what makes sense but a matter of what is legal, there are accounting rules around how you do things like expensing (rent, depreciating assets..etc) and revenue recognition (can't do it before you deliver service/goods)...I believe quarterly is the wall street standard, I am not sure there is a law requiring it but your shareholders will probably demand it.