How do you calculate net profit for Solo 401k contribution

I started working as a contractor in December, 2024. My income was $5,000. My business expenses were $3,000, including start-up costs. I understand that solo 401k contribution limits are calculated based on net profit from my tax Schedule C. How do I calculate net profit? Is my net profit $2,000 ($5,000 - $3,000)? If so, is the maximum contribution that I can defer into my solo 401k is $1,858?