Going through a separation is hard enough. Figuring out what you will owe, or receive, in child support should not make it harder. Here is the good news: in the United States, child support is not left up to a judge's gut feeling. Every state has a formula written into its own family law that turns your income, your co-parent's income, and how parenting time is split into an actual dollar figure. The bad news is that formula usually lives inside pages of legal code that almost nobody reads until they suddenly need to. That is the gap this page is built to close. Below is a plain-English breakdown of how the math actually works in your state, followed by a free calculator that turns those numbers into a real monthly estimate in under a minute.
Child Support Runs on a Formula, Not a Guess
Every state, plus Washington DC, has its own child support guidelines written into law. Judges are required to apply them in the large majority of cases, and can only move away from the guideline number for specific, documented reasons, such as a child's unusual medical needs or a parent's documented ability to earn more. That means the outcome in your case is far more predictable than most people assume, as long as you know which formula your state uses and you have accurate numbers to work with. The tricky part is that the formula itself is not the same from state to state, and in some cases it is very different, which is exactly why "how is child support calculated" is one of the most searched family law questions in the country.
The Three Formulas Used Across the US
Nearly every state falls into one of three systems.
The Income Shares Model is used by the large majority of states, including California, Florida, Illinois, Ohio, and Pennsylvania. Both parents' incomes are combined into one number, the state's schedule estimates what that combined household would typically spend raising the number of children involved, and that total is then split between the two parents in proportion to how much each one earns.
The Percentage of Income Model is used by a smaller group of states, including Texas, Wisconsin, Nevada, Alaska, Mississippi, and North Dakota. Instead of combining both incomes, this formula applies a set percentage directly to the paying parent's income, with the percentage rising as the number of children rises.
The Melson Formula is used only in Delaware, Hawaii, and Montana. It is the most layered of the three: it first protects a minimum amount for each parent to cover their own basic living costs, then calculates support out of what is left over, with an added allowance tied to the child's standard of living.
Knowing which model your state uses explains something that confuses a lot of parents: two people earning identical incomes in two different states can end up with noticeably different support numbers. That is not a mistake or an inconsistency. It is simply two different formulas doing two different jobs.
What Actually Moves the Number Up or Down
Whichever model your state uses, five inputs tend to matter the most.
- Both parents' gross monthly income
- The number of children covered by the case
- How many overnights each parent has with the children over the year
- The monthly cost of the children's health insurance
- Work-related childcare costs
Of these, parenting time is the one that surprises people the most. Most states reduce the paying parent's obligation once their overnight time crosses a certain threshold, often somewhere around 20 to 30 percent of the year, on the reasoning that a parent who has the kids more often is already covering more of the day-to-day costs directly. Two parents with identical incomes can end up owing noticeably different amounts depending purely on how the calendar is split between them.
Try the Free Child Support Calculator
Rather than trying to hand-calculate any of this from a state statute, the tool on this page does it for you. It covers all 50 states plus Washington DC, and it uses the exact statutory percentages for states like Texas, California, New York, Wisconsin, Alaska, Mississippi, and Nevada. For states that publish their guideline as a detailed table rather than a simple formula, it uses a clearly labeled estimate instead of guessing, so you always know how much to trust the number you are looking at. You enter both incomes, the custody split, and any health insurance or childcare costs, and it returns an instant monthly figure along with a full breakdown of how that figure was built. It is free, takes about a minute, and does not ask you to create an account.
Calculate My Child Support Estimate ->
How to Use the Calculator
- Select your state from the list
- Enter your monthly income and your co-parent's monthly income
- Choose the number of children in the case
- Set the slider to the actual number of overnights each parent has per year
- Add health insurance and childcare costs, if there are any
- Get your instant estimate, along with the full math shown underneath it
Common Questions
Is the number from this calculator legally binding?
No. This is an estimate based on published state guidelines, meant to give you a realistic starting point before you talk to a court, a mediator, or an attorney. Judges can adjust the guideline amount for documented reasons, and some deductions and credits are specific enough that only your state's official worksheet, or a licensed family law attorney, can give you a court-ready number.
Why did I get a different number than a friend in another state, even though our incomes look similar?
Because your states are almost certainly using different formulas, or different percentages within the same formula. Texas and Wisconsin, for example, both use a Percentage of Income Model, but the actual percentages and the way each state defines income are not identical.
Does it matter if I round the custody days up or down a little?
A bit of precision helps, but small differences of a few nights rarely move the outcome much. What matters far more is whether you cross your state's shared-parenting threshold, since crossing that line can trigger a meaningfully different calculation altogether.
Is my income or custody information saved anywhere?
No. The calculator runs the entire calculation inside your own browser and does not store or send your income or custody details anywhere.
Child support formulas exist so that outcomes are predictable and fair, not so that they stay mysterious. Once you know which model your state uses and which factors it weighs, the number stops feeling random. Use the calculator below to see where your case is likely to land, and treat the result as a starting point for a conversation with a family law attorney or your state's child support agency, not as the final word.