The concept of adjusted gross income is intimidating to many people, especially given how long and complex tax returns have gotten. Yet if you're like millions of Americans whose sole source of income comes from their job, you can typically calculate your adjusted gross income from your pay stub. Below, we'll walk you through the process, alerting you to situations where you might need to look elsewhere to get a complete picture of your tax situation.

AGI and you
The best pay stub to use to figure your AGI is the last one of the year, because it will typically have year-to-date totals that represent your entire income for the year. Most pay stubs have a line marked gross income, which includes not only your take-home pay but also any deductions that were taken out of your paycheck. This figure is the starting point for calculating AGI.

Elsewhere on your pay stub, you'll see deductions for various items. You can subtract only some of those items from your gross income to calculate AGI. For instance, the money that's withheld from your paycheck for Social Security and Medicare taxes, sometimes referred to as FICA on your pay stub, isn't deductible from gross income. However, if you have money withheld for deductible items like retirement plan contributions, health insurance premiums, or contributions to a flexible spending account, then those amounts do get subtracted in calculating adjusted gross income.

The best way to verify that your calculation is correct is to compare it against the figures on your year-end W-2 form, which your employer sends you in January. The W-2 shows gross income as well as breaking down allowed adjustments to income, helping you more directly calculate your AGI.

What else to include
It's important to remember that AGI includes not only job income but also income from other sources. If you have income from investments or a business you run on the side, you'll have to include it as part of your gross income and factor it into your AGI calculations.

Similarly, some adjustments to income won't show up on a pay stub but can still reduce your AGI. IRA contributions, student loan interest, and penalties for early withdrawal on bank CDs are just a few examples of items unrelated to your job that can reduce your AGI.

Using your pay stub is a good starting point for figuring your AGI. Depending on whether you have other outside considerations beyond your job, the numbers you get from your pay stub could be extremely close or even dead-on what your actual AGI turns out to be.

This article is part of The Motley Fool's Knowledge Center, which was created based on the collected wisdom of a fantastic community of investors. We'd love to hear your questions, thoughts, and opinions on the Knowledge Center in general or this page in particular. Your input will help us help the world invest, better! Email us at knowledgecenter@fool.com. Thanks -- and Fool on!

Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.