We adjust net profit for the deductible half of self-employment tax, then apply each plan's rules for 2025: a SEP-IRA and the employer side of a Solo 401(k) allow about 20% of adjusted profit; a Solo 401(k) adds an employee deferral of 23,500 (7,500 catch-up at 50+); a SIMPLE IRA allows a 16,500 deferral (3,500 catch-up) plus a 3% employer match. All are capped by the annual additions limit. Estimates only; confirm with a tax advisor.