Managing income and expenses is something too few self-publishing authors give enough attention. It is a rampant problem, and the self-publishing portals do not give a damn about you; they already got their cut off the top of your profits. We know of several such who did not have enough left over for legal counsel when they got in trouble.
More than a few times, we have seen (and shown) authors who spend more on promotion than they ever make in royalties. We have seen the same for authors working with professional publishers. The answer is rather obvious.
At the year’s end—and along the way—your need to generate financial reports whether doing taxes yourself or with a certified CPA to handle the complexities. As always, we advise being prepared with software to make your life easier so you can concentrate on writing.
You do not have to (re)pay to meet accounting needs and requirements. Two new cross-platform applications to serve your needs are now listed in “Resources: Finance.”