Base Tax at $100,000 (No Optimization)
2025 tax calculation — $100,000 net SE income, single filer, no retirement contributions
| Component | Amount |
|---|---|
| Net SE income | $100,000 |
| SE tax (15.3% × 92.35%) | $14,130 |
| SE tax deduction (50% of SE tax) | −$7,065 |
| Standard deduction (single 2025) | −$15,000 |
| QBI deduction (approx. 20% of QBI) | −$13,139 |
| Taxable income | $64,796 |
| Federal income tax (22% bracket) | $9,660 |
| Total federal tax liability | $23,790 |
| Effective total federal rate | 23.8% |
A self-employed worker earning $100,000 who maximizes a Solo 401k (employee contribution $23,500 + employer contribution $18,500 = $42,000) reduces their net SE income base, saving approximately $11,800 in combined federal taxes while building $42,000 in tax-advantaged retirement savings.
Optimized Tax at $100,000 (With Solo 401k)
Tax savings from retirement contributions at $100,000 SE income
| Scenario | Net SE Income (After 401k) | Total Federal Tax | Tax Savings vs. No 401k |
|---|---|---|---|
| No retirement contribution | $100,000 | $23,790 | — |
| IRA only ($7,000) | $93,000 (base unchanged for SE) | $22,770 | $1,020 |
| SEP-IRA ($18,500 max) | $81,500 effective base | $20,100 | $3,690 |
| Solo 401k employee only ($23,500) | $76,500 effective | $18,900 | $4,890 |
| Solo 401k max ($42,000) | $58,000 effective base | $12,100 | $11,690 |
A software consultant in Boston earning $100,000 who maximizes a Solo 401k saves $11,690 in federal taxes annually — while building $42,000 in retirement savings. The effective return on Solo 401k contributions (immediate tax savings) is approximately 28% at this income level. It is one of the highest-return financial moves available to self-employed workers.
Calculate Your Optimized Tax at $100K
Enter your income and planned retirement contributions to see your tax savings and total liability with optimization.