Split shared expenses by income

An income-based split — sometimes called a proportional split — gives each partner a share of a shared expense that matches their share of your combined income. The same two steps apply regardless of the currency or the expense.

This illustrative month applies the formula above to take-home incomes of $3,100.00 and $1,900.00 — a 62%/38% share — across three shared expenses.

A proportional split can help when partners have meaningfully different incomes and want each person’s contribution to track what they earn, rather than an equal dollar amount. Because the same income proportion applies to every shared expense, the partner with the higher income contributes a larger dollar amount, while the share of each partner’s own income going toward shared costs stays close to equal.

It can also simplify a household with several shared expenses: once you agree on each partner’s share, the same percentages apply to rent, groceries, utilities, or any other expense you decide to split this way.

Proportional splitting is not required for every expense, or for every couple. Some partners prefer equal dollar amounts regardless of income, particularly for costs both people use the same way. Others apply different methods to different expenses — for example, rent by income and a shared subscription 50/50.

To see the two methods side by side in dollars and in income share, you can compare 50/50 and proportional splitting. If you want to weigh all four common approaches, you can also choose a method for splitting expenses as a couple.

If income varies month to month — for example, with freelance work, commissions, or overtime — choose a comparable period before applying the formula, such as an average of recent months, and use that same period for both partners.

If only one partner has income, the formula assigns the full shared amount to that partner: a 100/0 split. It does not account for money either partner has already set aside, personal debts, unpaid care work, or other contributions a partner makes to the household.

If both incomes are zero, an income-based split cannot be calculated — there is no income proportion to divide the expense by.

Fairmony’s Smart Split applies this same income-based method to the expenses you record in the app. You can save an income-based split as the default for new expenses, or adjust a custom percentage for an expense that needs one. Each expense records who paid and each partner’s share, and Fairmony shows what is ready to settle between you.

This web calculator is separate from the app: figures you enter here are not transferred to Fairmony, and using it does not change any expense you have already recorded. To see what Fairmony records, visit the Fairmony home page.