There are a few things you should have on hand to calculate your take-home pay:
The amount of your gross pay. If you earn a fixed salary, this is easy to figure out. Just divide the annual amount by the number of periods each year. If you are paid hourly, multiply that rate by 40 hours to determine your weekly pay.
Your number of personal exemptions. When you start a new job, you fill out a W-4 form to tell your employer how much to withhold from your check. The number may be zero or one if you are single, or greater if you have dependents.
Your tax filing status. There are standard federal and state tax deductions that vary depending on whether you are single, married filing jointly, married filing separately, head of household, or a surviving spouse.
Other payroll deductions. This category could include contributions to a 401(k) retirement plan, health insurance, life insurance, or a flexible spending account for medical expenses. It also may include union dues or any other garnishments that are taken from your wages. It helps to categorize these according to pre-tax and after-tax contributions, to deduct them from either your gross salary or after-tax calculation.
Calculating Taxable Income
First, calculate your FICA taxes for the year, otherwise known as your contribution to Social Security and Medicare. Everyone pays a flat, 7.65 percent rate on the first $128,400 (as of 2018) of earned income. You can reduce the amount of your annual gross pay by this percentage before making other calculations.
Next, adjust your annual gross income by subtracting personal exemptions and standard deductions that the IRS gives you before it calculates your income tax. The personal exemption rate changes each year, so be sure to find current exemption rates when making your calculation. For every exemption claimed on your W-4 form, you will subtract the current rate from your gross income. So if the rate is $4,050 and you take one exemption, subtract $4,050 from your income. If you take two exemptions, subtract $9,000.
Your standard deduction is subtracted next. Standard deductions also change from year to year and are based on your filing status. You can find current standard deduction rates on the IRS website.
Once you’ve subtracted personal exemptions and a standard deduction, the resulting number should be very close to your taxable income. This is the total that will be used to determine your federal and state tax brackets.
Calculating Income Taxes
There are several taxes that may be applied to your gross pay, including federal, state, and even local income taxes.
The amount of federal tax you pay will depend on your filing status and bracket, which you can find in the Federal Tax Bracket tables updated annually by the Tax Foundation.
If you live in a state with a personal income tax, you will need to find your state tax bracket to determine how much will be deducted from your take-home pay. Each state has its own set of brackets which should be available on the state government website where you live. The Tax Foundation also lists recent state individual income tax rates and brackets on its website. It also includes information on local taxes, where they apply. New York City, for example, has its own tax on income.
Add together your federal, state, and other income taxes, and this is the amount that will be deducted from your paychecks over the course of the year.
Other After-Tax Payroll Deductions
Remember also to subtract any other relevant deductions. Depending on whether they are pre-tax or after-tax deductions, you can deduct them from your salary before or after calculating income tax due. For example, if you contribute 6 percent of pretax salary to a 401(k) retirement plan, take that amount from your gross salary before calculating your taxes.
Health insurance premiums paid by you are also typically taken from gross pay before taxes are taken out. For union dues and other garnishments, you can verify whether they are taken out before or after tax, or use estimates for those figures.
Final Calculations
To determine the total amount of money deducted from your paychecks, add up the amounts you've calculated FICA taxes, income taxes, and other deductions, then subtract that total amount from your annual gross pay. What's left is your net pay. Divide both your total deductions and your net pay by the number of pay periods for the year to determine how much those amounts will be per paycheck.