How much tax withholding is a good idea to keep for a small personal business on the side? Does 15% sound about right?
You will owe self employment tax (~15%) and regular tax (your individual tax rate) on the profit (revenue - expenses).
I don't know if I'm wording this right. Does placing 3rd party ads on your website constitute small business, or is it just taxed as additional income, like having a 2nd job...