Thank you for your responses. I do have a Roth IRA which I have already been maxing out. I don't currently report some of the income I make through music (outside of my 9-5) because it's usually very minuscule. However, I could easily register myself as a business, expand on my side earnings specific to music, and put that money into a solo 401k instead of putting it directly into a non tax-sheltered index fund. My question is whether or not that extra step is worthwhile or if I should just continue putting my extra change into a non tax-sheltered index.