I built an app to help me manage irregular income because I needed it myself. I don't know if anyone else does.

I have a main job but I also make money on the side, and the moment that started happening I realized I had no idea what I could actually spend. I've also been watching my brother, a full-time photographer, struggle with managing irregular income, never knowing how much he can safely spend, how much to set aside for bad months or even for taxes.
So I built kaden, an app that smooths irregular income into a stable weekly number to guide your spending, after taxes and recurring bills are set aside automatically. I built it because I would, and will, use it. But I know that's not enough.
If your income changes month to month, how do you actually manage it today?
Do you have a system that works? Did you figure it out yourself? Or is it mostly guesswork?
I'm genuinely trying to understand if this is a real problem for others or just something I've been overthinking.