To determine taxes on online income from display ads and affiliate commissions, you must first track all earnings accurately, including payments from platforms like Google AdSense or Amazon Associates. This income is typically considered self-employment income and must be reported on your tax return. In the U.S., you'll use Schedule C (Form 1040) to report profits and deduct business expenses. You may also owe self-employment tax, reported on Schedule SE. Keeping detailed records of expenses such as web hosting, software, and marketing helps reduce taxable income. If earnings exceed $400 annually, tax filing is required. Additionally, quarterly estimated tax payments may be necessary. Consult a tax professional for compliance with local, state, and federal tax laws.