Income-Proportional Bill Splitter for Couples

When one partner earns more, a straight 50/50 split on the bills can leave the lower earner with far less of their own pay. This spreadsheet splits shared bills in proportion to each partner's income instead, then does the part every couple actually argues about: it works out who pays who, and exactly how much, as a single settle-up transfer — no joint account required.

The four tabs include:

• This Month: names, incomes, the split method, bills and the settle-up figure
• Year Overview: a row per month so the fair share and settle-up figure update as incomes change through the year
• How Splitting Works: proportional vs 50/50 in plain English, plus UK council-tax notes
• A QA & Version tab showing the results

Put in both incomes and it calculates each person's fair share automatically, with 50/50 or a custom percentage available to compare. Mark who actually pays each bill and the sheet nets everything down to one settle-up figure using your own names; with a joint account, it shows what each of you should pay into the pot instead.

The maths is checked with 73 automated tests, including a negative account credit, an equal-income and a zero-income case, and a 12-month run with a payrise and the council-tax Feb/March gap — all independently re-checked. 73 of 73 checks pass.

This is a budgeting tool, not financial advice: proportional-to-income is one common approach to fairness, not a legal rule.