The contribution limit for the SEP IRA contribution is largely independent of the contribution limit for the Roth IRA. The only interaction is that the contribution to the SEP IRA reduces the compensation available to contribute to the Roth IRA. As long as net profit exceeds the sum of the deductible portion of self-employment taxes, the permissible SEP IRA contribution and the Roth IRA contribution, the contribution to one does not limit the contribution to the other. $10,760 of net profit would be sufficient to maximize both the SEP IRA contribution and the Roth IRA contribution. With less net profit than that you would have to limit your SEP IRA contribution to less than maximum permissible 20% of net earnings to avoid a portion of your $8,000 Roth IRA contribution being an excess contribution. Net earnings are net profit minus the deductible portion of self-employment taxes. With $10,760 of net profit from self employment, $760 would generally be the deductible portion of self-employment taxes, leaving $10,000 to be split between the maximum $2,000 SEP contribution and the $8,000 Roth IRA contribution.
