How couples can split shared costs fairly in a budget spreadsheet

Updated 2026-11-02 · Planners and templates · by CyberMax

Short answer

Most couples use one of three systems: split shared costs 50/50; split them in proportion to income (each pays their share of income × shared costs); or pool everything into one budget. For the proportional split, each person's contribution = their income / combined income × total shared costs.

Copy-paste code

Proportional split (B2 = your income, B3 = partner's income, B5 = shared costs)

Your share %:        =B2 / (B2 + B3)
You pay:             =B5 * B2 / (B2 + B3)
Partner pays:        =B5 * B3 / (B2 + B3)
Shared costs B5:     =SUM(Shared!B:B)       (rent, utilities, groceries...)

Good to know

Write down which costs are shared before choosing a split; the argument is usually about the list, not the maths.

General information, not financial advice.

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Questions

Example?

Incomes $5,000 and $3,000, shared costs $3,200: you pay $2,000 (62.5%), your partner pays $1,200.

Joint or separate accounts?

Many couples use a joint account for shared costs and keep personal accounts for the rest.

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