Two people share a flat. One earns 60,000 and one earns 30,000. Rent is 1,500 a month. Splitting it down the middle costs the first person 15 percent of their income and the second person 30 percent.
Same number, very different weight. Proportional splitting is the fix, and the maths is simpler than people expect.
The formula
Add both incomes. Work out each person's share of that total. Apply those percentages to the shared bill.
In the example above: combined income is 90,000. The first person earns 67 percent of it, the second earns 33 percent. So rent splits 1,005 and 495 rather than 750 each.
Both now pay 20 percent of their income towards rent. That is the whole idea: equal pain rather than equal pounds.
A worked example with three people
It scales without getting harder.
| Person | Monthly income | Share of total | Pays of a 1,800 rent |
|---|---|---|---|
| Alex | 4,000 | 44% | 792 |
| Bea | 3,200 | 36% | 648 |
| Cai | 1,800 | 20% | 360 |
| Total | 9,000 | 100% | 1,800 |
Round to whole units and give the remainder to whoever earns most. Nobody has ever fallen out over 40 cents, and precision to the penny makes the whole thing feel clinical.
What to apply it to, and what not to
This is where most attempts go wrong. Proportional splitting suits costs that are fixed, shared and unavoidable.
- Good candidates: rent, council tax, utilities, broadband, shared insurance, a joint food budget
- Poor candidates: a restaurant where people ordered very differently, holidays, gifts, anything optional
The reason is simple. Fixed costs are the price of existing in the household, so scaling them to income makes sense. Discretionary spending is a choice, and scaling choices to income means the higher earner subsidises the other person's preferences, which breeds resentment quickly.
For the discretionary side, item level splitting is usually fairer. We covered that in how to split a bill by items.
How to raise it without it going badly
The conversation is harder than the arithmetic, because it requires disclosing what you earn.
Agree the principle before anyone says a number. Ask whether you both think shared costs should scale with income. That is a question about values, and it is much easier to answer honestly than "how much do you make".
If you agree on the principle, the numbers follow naturally. If you do not, you have learnt something important without either of you having to defend a salary.
One phrasing that works well: "I would rather we both feel like rent is manageable than that we both pay the same number." It puts the goal first.
The variations worth knowing
Pure proportional is not the only option, and sometimes not the best one.
| Method | How it works | Suits |
|---|---|---|
| Equal | Everyone pays the same | Similar incomes |
| Proportional | Share of combined income | Clearly different incomes |
| Proportional after a floor | Each keeps a fixed personal amount first, then split the rest proportionally | Big income gaps where the lower earner has little slack |
| Fixed contribution | Lower earner pays a set amount, higher earner covers the rest | Very large gaps, or one partner between jobs |
The floor variant is worth understanding. If one person earns 1,200 and another 6,000, pure proportional still leaves the lower earner with very little discretionary money. Letting each person set aside a fixed personal amount first, then splitting the remainder proportionally, tends to feel fairer in practice.
Keep it stable
Do not recalculate every payday. Pick a review point, usually once a year or when someone changes job, and leave it alone in between.
Constant recalculation turns your household budget into a rolling negotiation, and the admin outweighs the fairness gained. A ratio that is roughly right and stable beats one that is exactly right and always changing.
Tracking it without a spreadsheet
Once the ratio is agreed, you need somewhere to log the bills so the split happens automatically.
EconoGlance handles unequal splits by percentage or exact amount, so you set the ratio once and every future bill follows it. See bill splitting, or splitting rent and bills with roommates for the household setup.
