I'm not sure I understand your question. Usually, when someone on itch donates a certain amount, it is registered in its entirety for the purpose of reaching the sale's goal, but it does not go entirely to the author. From that sum, itch's fees, payment systems's fees, and taxes are removed. Whatever is left goes to the author. Fees and taxes may depend on the amount processed, usually being more favorable for higher amounts. As for what I need, I don't have an answer. I appreciate every donation and they surely motivate me, but this is a pleasant hobby turned side gig for me, and I am happy with my work being appreciated and the community around it being healthy.
I hope this answers your question. If not, could you please rephrase it?