Your filing status: Whether you're single, married filing jointly, etc.
Income details: This includes your total income and details of any deductions or credits you're eligible for.
Information on taxes already paid: If you've had any federal income tax withheld or made estimated tax payments, you'll need these amounts.
Keep in mind, you don’t need to wait to have your final documents in-hand to use the calculator. You can use a pay stub instead. But having the actual documents will make the results more accurate.