Hi,

I am an one-employee S-corp and until now have only used a SEP-IRA.
But I have been looking for a way to save more re-tax for retirement + reduce my taxable income.
And came across Solo 401k (Individual 401k) and immediately thought that it would give me more potential to save pre-tax.

A few questions on the Solo 401k:

1) I believe I cannot contribute to a SEP and a Solo 401k in the same year (Both could be open though). Is that correct?

2) For the SEP, I employed a simple calculation for the employer’s SEP contribution.
Assume my compensation from my S-corp is 100K.
My SEP would be 25% of it, i.e. 25K.
Of course, outside of the above 125K, my S-corp would pay for FICA (not my FICA) and business expenses.
Now, in case of using a Solo 401k instead, will my calculations remain similar?
i.e. assuming same compensation, S-corp will be able to invest 25K to my 401k (doing same calculation as for SEP?).
And I believe I could invest an additional $18.5K ($24.5K if age > 50) from the 100k salary, as an employee portion.
Total of employer and employee portions must not exceed $55k ($61K if age > 50).
Please let me know if I need to employ the simple 25% rule I mention above any differently in the Solo 401k scenario.

3) I also believe the FICA in the Solo 401k scenario will be same as in the SEP.
Because my S Corp will continue to pay employer+employee (and cut from salary) FICA portions for 401k amounts too. Only difference: the 401k will be invested pre-tax so no Income Tax is payable.
Is the FICA (same as before) and Income Tax Payable (none) stated for 401k correct? Please confirm.

Thanks!