Do I owe taxes on money from selling online?

It depends on whether you are running a business or just cleaning out your closet. Selling personal items for less than you paid is generally not taxable, though selling for a profit can create a taxable gain. If you sell regularly to make money - on platforms like Etsy or eBay - that is business income you must report, and you can deduct related expenses. You may receive a 1099-K reporting your gross sales regardless. Keep records of what you paid and what you sold items for, and ask a professional if your activity is substantial.