Splitting Expenses When Incomes Differ
Parents assume shared expenses are split down the middle, because half is the intuitive number.
A great many orders say something else.
Pro rata by income
The common alternative is a split in proportion to each parent's share of the combined parental income.
If one parent earns $80,000 and the other $45,000, their combined income is $125,000. The first earns 64% of it, the second 36%. A $500 orthodontic bill divides $320 and $180 rather than $250 each.
The logic follows the same reasoning as the support formula itself: children's costs should fall on the parents in proportion to their capacity to meet them.
Check what your order actually says
This is the practical point of the whole page. Orders commonly use one of:
- 50/50, regardless of income
- Pro rata, with the percentages either stated or recalculated periodically
- A fixed split that is not 50/50 — 60/40, 70/30 — set at the time of the order
- One parent pays a defined category entirely, with the other covering something else
Parents frequently operate on the wrong assumption for years, and discover it during a dispute. Read the clause before you need it.
The problem with pro rata: it goes stale
A percentage set from 2022 incomes is a percentage from 2022. People change jobs, get promoted, go part-time, start businesses.
Better-drafted orders handle this with a recalculation trigger — annually, or on exchange of tax returns, or when either income changes by more than some percentage. If your order fixes the percentage with no mechanism to revisit it, that percentage stands until someone moves to change it.
If your order requires an annual exchange of income information and you have not done one in three years, you both have a problem and neither of you is in a strong position to complain about it.
Rounding, and the thing not to do
Pro rata splits produce awkward numbers. $180.40. $63.72.
Two suggestions. Agree in advance to round to the nearest dollar, which removes a category of pointless friction. And do not net expenses off against each other informally across months unless you both track it identically — one parent's running total in their head is the most common source of "you still owe me."
Settle each expense as its own item, or settle on a fixed date each month. Either works. Mixing them does not.
Where Civly fits
Civly splits at whatever percentage your order actually sets, not an assumed half. Set it once and every expense divides correctly, with the split shown on the request so both parents can see the arithmetic rather than reproduce it.
Each expense carries its receipt and its own approve, dispute or paid status, so nothing depends on a running total either of you is keeping privately.
If your order requires an annual recalculation, the percentage is a setting you change — the historical expenses keep the split that applied when they were incurred.
This is general information, not legal advice. How shared expenses are divided depends on your own order and on your state's law. Talk to a family law attorney licensed where you live.