In the US, if your income is more than $600 per month, the IRS will require you to make estimated quarterly tax payments. You can do this by filling in Form T (quarterly taxes). When filling in this form, it is important to keep track of the total income that has been received for that quarter. You can then deduct specific eligible expenses (like business use of home) from your taxable gross income before working out how much tax you should pay. If you are not required to make quarterly tax payments (because your monthly affiliate income is too low) then simply pay the total amount due for that year on or before April 15th of the following year.