Making estimated tax payments means that you need to estimate how much income you’re likely to make for the year and determine how much you will owe to the IRS for income taxes. You can use IRS Form 1040-ES to calculate how much tax liability you’ll have for the year. IRS Publication 505 contains all the rules and details you might need to know about how to calculate this amount. If you overestimated how much tax liability you’d owe for a year and are due a refund, you can choose to receive that money now or apply the overage to the following year’s quarterly tax payments.