As a divorced parent, you'll still have a legal obligation to support your children if you get married again. And either parent's remarriage won't, by itself, lead to a change in the amount of child support for those kids. In Missouri, however, you might qualify for a child support modification based on certain changes in your financial situation that result from having a new family.
The guidelines for calculating child support in Missouri are complicated. The underlying principle is that the total support obligation is based on both parents' income, and each parent is responsible for a share of that obligation based on their proportionate share of their combined incomes. Usually, the noncustodial parent (the one with the kids less than half the time) pays child support, while the custodial parent pays directly for the children's day-to-day needs. The guidelines include various adjustments—including one that accounts for noncustodial parents' additional expenses when they have significant parenting time under their custody orders.
Missouri presumes that the amount of child support calculated under the guidelines is the correct amount. But a judge may order a different amount (a "deviation") if it would be unfair or inappropriate to use the calculated amount, based on the specific circumstances in the case. (Mo. Rev. Stat. § 452.340.9 (2024).)
If parents want to change an existing child support order, they'll need to prove that they've experienced a change in circumstances that's continuing and is substantial enough to make the existing amount unreasonable. (Mo. Rev. Stat. § 452.370 (2024).)
When Missouri judges are deciding whether there's been a change in circumstances warranting a modification of child support, they must consider both parents' financial resources—including the extent to which a parent's new spouse or live-in partner is sharing their "reasonable" expenses. (Mo. Rev. Stat. § 452.370.1 (2024).)
This means that if your ex has a wealthy new spouse who's making a significant contribution to their shared expenses, that may qualify as a change of circumstances. But that doesn't mean the new spouse's income will necessarily result in a different amount of support.
Why is that? As Missouri courts have pointed out, a new spouse's contribution to expenses is relevant to the question of whether there's been a change of circumstances—but not to the actual calculation of child support. After a parent has met the threshold changed-circumstances requirement for a modification request, the judge must then apply the guidelines to decide on the correct amount of support. Under those guidelines, a new spouse's income is not included in a parent's income when calculating support. (Mo. Rev. Stat. § 452.370.2 (2024); Gal v. Gal, 937 S.W.2d 391 (Mo. Ct. App. 1997).)
Despite this apparent contradiction between the requirements for a modification and a new support calculation, you could potentially convince a judge to deviate from the standard calculation based on the fact that your ex has additional financial resources because of a new spouse's income. The parents' resources are one of the factors judges must consider when they're deciding whether the guideline amount of support would be unfair or inappropriate. But a judge will also consider the children's needs, as well as the other parent's needs and resources. So the ultimate decision will rest on the judge's view of the overall picture and what's best for the children. (Mo. Rev. Stat. § 452.340.9 (2024).)
When calculating child support in Missouri, parents may subtract certain obligations from their gross income, including their support obligation for other children who are primarily living with them. This adjustment, which works like a credit, applies to natural or adopted children from a new marriage—but not to stepchildren.
However, the effect of this credit will depend on which parent has requested a modification in the current amount of support, and whether a new calculation results in an increase or a reduction in the support amount.
Apparently, this means you won't be able to get credit for supporting new children from your remarriage as a way to lower support that you're paying for children from a previous marriage. However, the credit may apply if your ex seeks to increase support (and the new calculation shows an increase). That also works in reverse: A parent who's receiving support payments may not use the credit to raise those payments.
(Samples v. Kouts, 954 S.W.2d 593 (Mo. Ct. App. 1997).)
Unless you and your ex can agree on a change to your existing child support order, you should at least speak with an attorney if you think you're entitled to a modification after your remarriage or your ex's. Modification requests can sometimes lead to surprising results. You might think you're entitled to lower the payments you've been paying (or raise the support you're receiving), only to have the judge do the opposite after considering your ex's financial situation and your children's needs.
An experienced, Missouri family law attorney should be able to explain how a judge is likely to view your request, in light of the law, previous court decisions, and the specific circumstances in your case.