A 1099 mobile app developer in Kentucky pays a flat 3.5% state tax on net profit, stacked on federal income tax and the 15.3% self-employment tax a W-2 employer would have split with you. Kentucky’s flat rate fell to 3.5% for 2026, though many counties add an occupational license fee on net profit, and every dollar of devices, store fees and test hardware you document on Schedule C cuts all three bills at once.