If you don’t know how the IRS determines how much money you get with a second stimulus check, it’s time to find out. The agency uses a pretty complicated formula (it was hard-baked into the stimulus bill, in fact) that starts with your taxes. If you’re one of the tens of millions of people eligible for a second stimulus payment, your second check total relies on equations that involve your AGI and how many dependents you can claim.

That may be the “simple” answer to the stimulus check question, but it isn’t the complete picture. Another layer beneath that is a formula that’s actually written into the language of December’s stimulus bill — and it could be the same one used in the next stimulus package to decide how much you’d get with a third stimulus check. This equation is what’s ultimately used to calculate how big a stimulus check the US Treasury will — or has — cut in your name.

An important thing to remember about the second stimulus check is that it uses the same equation as the first one. Due in part to the $600 income limit with the new check, some people weren’t eligible this time around, simply because of the way the formula works. Others may still qualify, but for a smaller portion of the stimulus money than people who meet the exact same eligibility requirements. (By the way, here’s how to claim any missing stimulus money in your 2020 taxes, and how to know when it’s time to initiate a payment trace.) This story was updated.

How the IRS calculates your stimulus check amount: Key detail

The two major variables being plugged into the equation are your adjusted gross income you put on your 2019 federal tax returns into a formula, and the number of eligible child dependents you claim. If the result is under a maximum limit, you will receive at least some stimulus check money. If the number is above it, you won’t receive any. (If you don’t typically file taxes, here’s what you need to know.)

There’s a sliding scale involved. As with the first check, if your adjusted gross income, or AGI, is less than $75,000 as a single taxpayer (that means no kids), you’ll receive the entire second stimulus check total of $600. If you made more than that, the size of your check would diminish until it hits the income limit, after which point you’d be ineligible.

This is the same equation that the IRS used for the first, $1,200 stimulus check. But the fact that this check is $600 actually lowers the maximum income limit you could hit, which means that more people will reach that limit sooner. A $600 flat payment for children 16 and younger could help mitigate your overall total (more below, it gets complex). 

This chart helps illustrate the income limits and the difference between the first and second stimulus checks.

How does it work when you add $600 for each kid?

This is where the calculations get really interesting. The numbers in the chart above don’t include the $600 flat rate for child dependents in the second stimulus check (this is up from $500 with the first stimulus check). There’s no cap on the number of child dependents that count toward your total check, as long as they’re younger than 17 years old. 

The IRS’ equation begins with the largest amount you’d be eligible to receive ($600 per single taxpayer or $1,200 for joint filers), and adds $600 for each qualifying child. Then it reduces the total possible sum according to your AGI.

It’s a little like starting a test with a perfect 100 point score and subtracting every point you “miss,” rather than starting with zero points and adding them all up at the end of the test.

But in this case, the dependents you name can start you at a higher value, say 110 points in our classroom example. So by the time you subtract “points,” you may still get more than people who don’t have dependents — even if your AGI is above the maximum cap. The more child dependents you have, the higher your starting value, and the higher your ending value, too.

That’s why it’s possible you could be out of range for a payment based on your AGI, but still receive a partial payment on the strength of your eligible dependents. Still confused? We don’t blame you. You can experiment with ranges in our second stimulus check calculator and see below for more sums.

See the stimulus payment formula in action here

We want to show you the calculation at work, and how the math changes for people who claim dependents. 

Remember that with the second check, an individual can qualify for a stimulus check of up to $600, a married couple who file taxes jointly can get up to $1,200 — and there’s an extra $600 per qualified child dependent. Note that a head of household is someone who files taxes individually and has at least one dependent. People who are considered single filers claim no dependents on their taxes, only themselves, which is why this group isn’t explicitly included in the chart below. 

These figures are based on the rules set out for the second stimulus check, worked out using Crumpe’s stimulus check calculator. They’re best considered estimates only, since secondary qualifications that could determine your final sum. If the amount below looks higher than what you receive, though, you may need to investigate a catch-up payment from the IRS.

How will the calculations for a third stimulus check work?

President Joe Biden has already laid out his proposal for a stimulus bill package that could yield a third stimulus check for as much as $1,400 or $2,000 per eligible adult (it might get complicated). If it comes to pass (maybe in February or March), the pattern of the first two checks indicates that, for the sake of simplicity, a future bill could once again direct the IRS to use the same formula. 

This is important, because it means:

• People who got the first two checks would get more money (because the $1,400 or $2,000 upper limit is higher).
• More people could qualify because the income limit threshold would rise, which would also raise the cutoff point for receiving no payment at all. We talk more about that here.

If the formula were to change in a way that also changes the income limit threshold, that might mean that fewer people in the higher-earning bracket would qualify for the $1,400 or $2,000 check. Right now, we aren’t hearing discussions around this topic.

Biden’s stimulus plan also seeks to change stimulus check qualifications that would increase the family’s overall pool for tens of millions of people, including money for dependents of any age, and for families with “mixed-status” citizenship. Remember, the bigger the sum a family starts with, the bigger the check they are likely to receive after the IRS makes its deductions based on your AGI. 

For more information, here are the top things to know about stimulus checks. And see how SSDI recipients and checks, older adults and retirees and people who aren’t US citizens or Americans who don’t live in the US can also qualify.