Deferrals > net s/e comp

I found a somewhat related post here, but what I've got is a little different.

One-person plan, Roth deferrals and profit sharing.  The sole prop (who is age 50+) has 2023 net Schedule C income of $29,000, and he wants to max.  My pension software tells me that his 1/2 FICA is $2,100 (rounding), therefore net compensation is $26,900.

Can he do the entire $29,000 as Roth deferrals?  I think it triggers the catch up rule that it can't cause a failure in the year allocated... but I've never seen it applied to 100% of compensation.

If not, I can split it and make some as profit sharing, but it would be simpler to be able to have it all one money type.

Thanks!

He can not defer more than 100% of compensation, you can't defer what you didn't make but an employer allocation can bring him over 100% but it being a sole prop...

With such low comp the math gets circular if you are trying to do the absolute max. You'll need to do a PS contribution first which can't exceed the 25% deduction limit so using your $26,900 figure you get a $5,380 PS contribution which reduces his pay to $21,520 of which he can deffer 100% and the last $5,380 would be catch up. For a total of $26,630. Or he could do no PS and contribute the full $26,900 as deferral.

It doesn't matter if the deferral is traditional, ROTH or a mix.