Substantial Gainful Self-Employment

I’m significantly disabled, and am applying for TPD. My doctor is happy to certify, as she knows how wrecked I am. I’m a bit confused about how to determine what qualifies as “substantial gainful employment” as I’m self-employed and work (part time and getting less and less) as a screenwriter.

Last year I made just under the cap (about $1550 per month) in income, but as a hobby I wrote a novel on the side, and the novel won an award that came with a monetary prize that would put me over the $1690 per month limit. I know I have to declare the prize as income on my taxes, but this wasn’t money from employment and was also a one-off – it’s sure not happening again. Would this be considered part of my employment, or would it be passive income like a royalty, and thus not included in the consideration?

Would it be better to wait another year so that the prize doesn’t make my earnings look bigger than they are?

Also, how do they determine what your ordinary and business expenses are? Or am i just supposed to estimate that and attest whether it’s under the limit? I file my taxes jointly with my spouse so I’m not sure how they’ll determine from our 2024 taxes what counts as my business expenses versus my spouses?

Any help appreciated, really want to make sure I get this right!