How to Calculate Tax on Business Income | The Motley Fool Here's how to use a common business expense, payroll taxes. Start with your typical employee's salary, and calculate how much you actually pay in payroll taxes. How to Use the IRS Tax Calculators: Taxable vs. Non-Taxable Income, Tax Filings and Tax Withholding The IRS Tax Calculators tell you how much taxable income you pay, with and without tax withholding. They can save you loads of time and money, too! What if you don't have any dependents? When you file your tax return, you'll notice that you need to report your dependents, even if they're listed as “other.” This means that you may need to include your spouse in order to file your tax return. And by “including your spouse,” we mean that you may also need to include him or her on any form that reports your tax. How is this calculated? If your spouse is not listed on your individual tax return, the IRS takes into account that fact and reports your taxable income. If you are married filing jointly, the IRS takes into account your spouse's income, and takes into account the tax filing status of each spouse. In other words, your spouse's income is not disregarded as much as your own, but your spouse's tax status is. This means that it pays to be listed as a head of household, and that you don't necessarily need to have the same income as your spouse to calculate his or her share of the cost of living. If one of you has a significant asset, like a home or a car, the IRS takes into account both your income and all your dependents' income as well. If the non-depreciating asset you own for your own use, you have to determine the depreciation tax it cost you in taxes by multiplying it by your adjusted gross income. As you can probably tell, there is a significant number of ways you can report or don't report to the IRS. So the key here is taking the time to understand the tax system and use the system to your advantage. For more on the IRS and tax accounting, check out these resources.