Thank you for the detailed and quick answer.
Seems two advantages for using the elective deferral first and the profit sharing later.
1. If one has a Roth provision, elective portion is the only way to use the Roth advantages.
2. It seems from the answer above that contributing first to elective portion helps maximize the available limit. Do net earnings depend on the amount contributed to the elective portion? If not, it is not clear to me why the total allowed limit will change with contributing first to the elective portion. Regardless, there seems to be no disadvantage to first using the elective portion.
Another advantage I can think of: Since exact profit sharing limit may not be calculated until actual tax filing, one can safely contribute the elective portion before Dec 31 (assuming income is well above the 18,000 IRS limit for 2017).
Follow up question: Seems I will be paying medicare tax on the solo-401k contribution regardless of whether it is classified as elective or profit sharing, is that right? Or can medicare tax be avoided in one of the classifications?
