Parents price a second child at double the first. Federal spending data says otherwise: housing, transport, food, and healthcare for an additional child run at a fraction of a first child's cost, while childcare stacks at close to full price and the FSA and child-tax-credit caps do not scale at all. Enter your current monthly baseline and the new-child costs you have quoted, and this tool stacks the true marginal: monthly, 18-year, and the cheapest lever you can pull.
Each factor is what an additional child costs as a share of your current spend in that category, per the USDA two-child ratios. Childcare is absent by design: it does not scale like the other categories, so it is priced directly in the next card. The child tax credit is a flat amount per child and the dependent-care FSA is a flat household cap, so neither scales either.