Compute AGI from gross income and above-the-line adjustments.
AGI
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Gross income
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Total adjustments
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The single number the rest of your return hangs on
Adjusted gross income is the hinge of the entire 1040. It sits between your total income and your taxable income, and it is the figure the IRS and dozens of other programs reach for when they need one clean measure of what you earn. Your eligibility for a Roth IRA, the size of your child tax credit, whether your student loan interest is deductible, your Medicare premium surcharges through IRMAA, and your ACA marketplace subsidy all key off AGI or a close cousin of it. Get AGI wrong and a chain of downstream numbers moves with it. That is why it earns its own dedicated line, line 11 on Form 1040.
This calculator builds AGI the way the form does. It totals your income from wages, interest and dividends, capital gains, and anything else, then subtracts the handful of deductions the tax code lets you take before AGI is struck. Those are the above-the-line adjustments, reported on Schedule 1. The phrase "above the line" simply means above the AGI line, and these deductions are valuable precisely because you get them whether or not you itemize.
Above-the-line beats below-the-line, and here is why
A dollar deducted above the line lowers AGI itself. A dollar deducted below the line (the standard deduction or itemized deductions) only lowers taxable income, after AGI is already locked. Because so many phase-outs and thresholds are measured against AGI, an above-the-line deduction does double duty: it cuts your tax and it can simultaneously requalify you for a credit or a contribution you were about to lose. The classic examples are a deductible traditional IRA contribution, the deductible half of self-employment tax, HSA contributions, and up to $2,500 of student loan interest.
Walking the default numbers from gross to AGI
The preloaded inputs show a wage earner with a little investment income and one adjustment. Here is the exact chain the tool computes.
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The HSA contribution does more than shave $3,000 off income. By pulling AGI down to $124,000 it nudges you further below the phase-out ranges for things like the Roth IRA, which begins phasing out for a single filer well above this level but tightens fast for higher earners. This is the lever most people underuse at tax time.
AGI, MAGI, and the trap people fall into
AGI is not always the figure a given rule uses. Many provisions use modified AGI, which takes your AGI and adds certain items back. The add-backs differ by purpose, which is the genuinely confusing part. For the Roth IRA contribution limit, MAGI adds back any deduction you took for a traditional IRA. For the student loan interest deduction, MAGI adds back that same interest deduction and any foreign earned income exclusion. There is no single MAGI. The common mistake is computing one MAGI and reusing it everywhere. Always check which add-backs the specific credit or limit calls for. IRS Publication 590-A spells out the MAGI definition for IRA purposes, and each credit's instructions define their own.
Where do I find last year's AGI?
It is line 11 of your prior-year Form 1040. The IRS uses it to verify your identity when you e-file, so you will be asked for it every filing season. If you cannot find the return, pull a free tax transcript from your IRS online account rather than guessing, because an AGI that does not match will cause your e-filed return to reject.
Does AGI include my 401(k) contributions?
No, and that is the point of a pre-tax 401(k). Traditional 401(k) deferrals are removed from your wages by your employer before your W-2 box 1 figure is even printed, so they never appear in the income you start from here. That is different from a traditional IRA, which you deduct as an explicit above-the-line adjustment. Both lower AGI, but only one shows up as a line you enter yourself.