1. Go to Wages and Income -> Other Business Situations -> Self-Employment Retirement Plans.
2. Answer Yes to making a self-employed retirement plan contribution.
3. Answer No to Individual or Roth 401(k).
4. Answer Yes to Keogh, SEP and SIMPLE contributions.
5. Mark the Maximize box for a SEP contribution.
TurboTax will automatically calculate the maximum permissible SEP contribution based on your net earnings from self-employment.