The bare-minimum bookkeeping setup that keeps Schedule C painless every April — and the signal that says it's time to upgrade to an S-Corp.
Set aside 25–30% of net profit and pay quarterly via Form 1040-ES (Apr 15, Jun 15, Sep 15, Jan 15).
When net profit consistently exceeds ~$70,000/year, S-Corp election usually saves $5,000–$15,000+/year. See S-Corp vs Sole Proprietor.