Retirement tax questions

Is this reported on Schedule C as Self-Employment income or some other business model?

According to the IRS:

"If you are self-employed (a sole proprietor or a working partner in a partnership or limited liability company), you must use a special rule to calculate retirement plan contributions for yourself. 

Retirement plan contributions are often calculated based on participant compensation. For example, you might decide to contribute 10% of each participant's compensation to your SEP plan. This formula works to determine employees' allocations, but your own contributions are more complicated. You can't simply multiply your net profit on Schedule C by 10%. 

You calculate self-employment (SE) tax using the amount of your net earnings from self-employment and following the instructions on Schedule SE, Self-Employment Tax. However, you must make adjustments to your net earnings from self-employment to arrive at the amount of "plan compensation" to use to determine the plan contribution/deduction for yourself.

Plan compensation for a self-employed individual

To calculate your plan compensation, you reduce your net earnings from self-employment by:

• the deductible portion of your SE tax from your Form 1040 return, Schedule 1, on the line for deductible part of self-employment tax, and
• the amount of your own (not your employees’) retirement plan contribution from your Form 1040 return, Schedule 1, on the line for self-employed SEP, SIMPLE, and qualified plans.

You use your plan compensation to calculate the amount of your own contribution/deduction. Note that your plan compensation and the amount of your own plan contribution/deduction depend on each other - to compute one, you need the other (this is a circular calculation). One way to do this is to use a reduced plan contribution rate. You can use the Table and Worksheets for the Self-Employed (Publication 560) to find the reduced plan contribution rate to calculate the plan contribution and deduction for yourself."