Is 50/50 actually fair?
Calculate a co-parenting expense split based on income — the same proportional method used in child support guidelines.
Enter both incomes to calculate a proportional split — defaults to 50/50 until you do.
The income-shares model — used in child support guidelines nationwide.
Most co-parents default to splitting expenses 50/50 — it's simple, and feels even-handed. But when one parent earns significantly more than the other, a flat 50/50 split puts a much heavier burden on the lower-earning parent relative to their income.
The income-shares model — the basis for child support guidelines in most U.S. states — instead splits costs in proportion to each parent's income. If you earn 65% of the household's combined income, you cover 65% of shared expenses. It's not about the higher earner being penalized — it's about both parents feeling the cost equally, relative to what they can afford.
You earn $6,000/month. Your co-parent earns $3,000/month. Combined income: $9,000. Your share: 67%. Their share: 33%. For a $300 orthodontist bill, you'd pay $200 and they'd pay $100 — instead of $150 each.
FairSplit applies your split ratio automatically — to every expense, every time.
Set your split once based on income, custody time, or your own agreement. FairSplit does the math, sends the request, and keeps the record — no spreadsheets, no arguments about percentages.
Get Early AccessQuestions about splitting co-parenting expenses fairly.
Many family courts use an 'income shares' model — each parent contributes to shared child expenses in proportion to their income, not a flat 50/50 split. If one parent earns 70% of the household's combined income, they cover 70% of shared expenses.
Not when incomes are significantly different. A 50/50 split can leave the lower-earning parent covering a much larger share of their income for the same expense. Proportional splitting based on income keeps the burden relative to each parent's ability to pay.
Use gross monthly income (before taxes) for the most accurate comparison — this matches how most state child support guidelines calculate income shares. Net income works too, as long as both parents use the same basis.
No. This tool is for informal estimates only. Your custody order or parenting plan may already specify a different split — always defer to your legal agreement. For a formal calculation, consult your state's child support guidelines or a family law attorney.
Yes. FairSplit lets you set a custom split ratio once — based on income, custody time, or any agreement — and applies it automatically to every expense you log, with no manual math required.