Household Expense Split Calculator: 64/36

A household expense split calculator follows a single rule: each person pays the share of costs that corresponds to their share of the joint net income. With 3,200 € and 1,800 € net, that amounts to 64% and 36%, meaning 1,280 € and 720 € out of 2,000 € in monthly costs.

Proportional cost splitting is a distribution model where both partners contribute the exact same percentage of their own income to the household rather than the same euro amount. With a 50/50 split, the person earning 1,800 € net pays 1,000 €, which is 55.6% of their salary.

You do not notice this on the first of the month. You notice it on the twentieth.

Key takeaways

• Formula: Own contribution = joint household costs × own net income ÷ joint net income. In Excel: =B2/(B2+C2)*D2.
• With proportional splitting, both partners pay the exact same percentage of their income, 40% in this example (2,000 € costs ÷ 5,000 € total net income).
• With a 50/50 split, the higher-earning person has 2,200 € left over while the other has only 800 €. Proportional splits leave them with 1,920 € and 1,080 € respectively.
• If income fluctuates, calculate using the average of the last three months; for a marginal job (earnings limit 2026: 603 € per month), the pure percentage formula reaches its limit.
• Checking takes ten seconds: contribution ÷ net income must yield the exact same result for both individuals.

Why 50/50 is rarely fair with unequal incomess

In a 50/50 split, both pay the same amount but do not carry the same burden: with 3,200 € net, a 1,000 € household share takes up 31.25% of income, whereas with 1,800 € net, it takes up 55.6%. The only thing that is equal is the number on the transfer slip. The financial wiggle room left over afterward differs by nearly a factor of three.

The consequences are quiet. No one argues about rent. The arguments are about the weekend trip to Hamburg that one person can easily afford and the other cannot, about the restaurant that is "not that expensive after all," and about the partner who "never has any money."

This is not a matter of character. This is mathematics. Anyone who puts 55.6% of their net income into the shared household is left with 800 € for clothes, mobile phone, retirement savings, and leisure. Anyone who pays 31.25% has 2,200 €.

There are three common models for couples with a noticeable income gap:

1. 50/50: Equal euro amount. Simple, but only fair when incomes are similar.
2. Proportional to net income: Equal percentage of income. The standard that Finanztip also discusses as an alternative to 50/50 for unequal salaries.
3. Equal fun money: Both incomes go into one pot, all costs are paid from it, and the remainder is split equally. Highly solidaristic, but with pitfalls (more on that below).

None of these is objectively correct. But only one can be justified in a single sentence: We both contribute the same share of what we have.

What is the formula for splitting household expenses fairly?

The formula has three ingredients: person A's net income, person B's net income, and the sum of the joint monthly costs. Contribution A = costs × net income A ÷ (net income A + net income B). Person B pays the rest. No calculator needs anything more, whether it is a spreadsheet, a notepad, or an app.

Step by step:

1. Add up net incomes. 3,200 € + 1,800 € = 5,000 €.
2. Calculate income shares. A: 3,200 ÷ 5,000 = 0.64. B: 1,800 ÷ 5,000 = 0.36.
3. Sum up joint costs. Only include what you genuinely use together. In the example, 2,000 €.
4. Multiply costs by the share. A: 2,000 × 0.64 = 1,280 €. B: 2,000 × 0.36 = 720 €.
5. Round and cross-check. 1,280 + 720 = 2,000. It matches.

In a spreadsheet, put A's net income in B2, B's net income in C2, and the costs in D2. Then =B2/(B2+C2)*D2 calculates A's contribution and =D2-E2 calculates B's (assuming E2 contains the first result). No estimation, no gut feeling. Deterministic mathematics: the same numbers always yield the same outcome.

A second calculation example for verification is provided by Familienservice with 3,000 € and 2,000 € net: a 60/40 ratio where, out of 1,500 € in household costs, A pays 900 € and B pays 600 €. If you plug these numbers into the formula and arrive at the same result, your calculator works. If you prefer a ready-made tool over your own spreadsheet, you can find criteria in our overview of online bill-splitting calculators.

How does the calculation look with 2,000 € in costs and 3,200 € to 1,800 € net?

With 3,200 € and 1,800 € net and 2,000 € in joint costs, person A proportionally pays 1,280 € and person B pays 720 €; both thus contribute 40% of their income. In a 50/50 split, it would be 1,000 € each. The total sum left over for both of you after household expenses is identical in every model: 3,000 €. It is purely about distribution.

	Person A	Person B	Total
Net income	3,200 €	1,800 €	5,000 €
Share of total net income	64%	36%	100%
Proportional contribution	1,280 €	720 €	2,000 €
Burden as % of own net income	40%	40%	–
Remainder after household (proportional)	1,920 €	1,080 €	3,000 €
50/50 contribution	1,000 €	1,000 €	2,000 €
Burden as % of own net income	31.25%	55.6%	–
Remainder after household (50/50)	2,200 €	800 €	3,000 €
"Equal fun money" contribution	1,700 €	300 €	2,000 €
Remainder after household (fun money)	1,500 €	1,500 €	3,000 €

Three things stand out.

First: Switching from 50/50 to proportional costs person A 280 € per month. Person B has 280 € more. That is the entire difference. No drama, but 3,360 € over the course of a year.

Second: Proportional sits between the extremes. Person A still keeps significantly more (1,920 € compared to 1,080 €). Whoever earns more also has more left over. Most higher earners find this fair.

Third: With equal fun money, A bears 85% of the household costs. This often works well in marriages with a shared life plan. For unmarried couples with a joint account, it can become tax-sensitive (see FAQ).

Which expenses belong in the household expense calculator?

The calculator should only include costs that both utilize equally: warm rent, electricity, internet, groceries, drugstore items, and shared insurance such as personal liability or household contents. Mobile phone contracts, clothing, hobbies, a car driven by only one person, and old debts stay out. Mixing personal items skews the percentage.

Here is how the 2,000 € from the example could be composed (example values, not average figures):

Item	Monthly
Warm rent	1,300 €
Electricity	90 €
Internet	40 €
Groceries	450 €
Drugstore items, cleaning supplies	50 €
Liability and household contents insurance	30 €
Reserve for repairs, miscellaneous	40 €
Total	2,000 €

Warm rent here amounts to 26% of the joint net income. Finanztip suggests as a guideline that warm housing costs should not exceed 30 to 35% of the household net income. If you are significantly above that, even the fairest formula helps only to a limited extent: then the budget is too tight, not the split incorrect.

Gray areas that you should clarify once:

• Streaming services: shared if both watch. Otherwise personal.
• Pet: shared if it is a joint pet.
• Home office: If one person needs a separate room for remote work, they can bear that rental share upfront by themselves. The rest is split proportionally.

What to do with fluctuating salaries or marginal jobs?

When income fluctuates, use the average of the last three months instead of a single month. If person B earns 1,200 €, 2,400 €, and 1,800 €, calculate with 1,800 € and you end up back at 720 €. Recalculating monthly is more precise, but creates a new transfer amount and new discussions every single month.

Fluctuating salary: Average or monthly statement?

The three-month average has a clear advantage: the standing order remains unchanged. You adjust it once per quarter. For self-employed individuals with highly irregular income, a longer period (six months) may be more sensible. Monthly recalculation is only worthwhile if fluctuations are large and unpredictable, such as with commissions.

Parental allowance, sick pay, or unemployment benefits count as net income. They are what actually lands in the account.

Marginal job: Where the formula breaks down

Suppose person B works a marginal job during studies or additional training and earns 600 € net. Person A continues to earn 3,200 €.

	Person A	Person B	Total
Net income	3,200 €	600 €	3,800 €
Share	84.21%	15.79%	100%
Proportional contribution	1,684.21 €	315.79 €	2,000 €
Burden as % of net income	52.6%	52.6%	–
Remainder after household	1,515.79 €	284.21 €	1,800 €

Mathematically correct. Practically, person B is left with 284 € for everything personal. That is hardly livable.

Two clean solutions:

1. Agree on minimum fun money. You specify that each person keeps at least a certain amount, such as 500 €. B then pays at most 100 €, and A covers 1,900 €. You define this limit together; no calculator can do that for you.
2. Switch to equal fun money. Total remainder 1,800 €, 900 € each. A bears the 2,000 € household costs completely and additionally transfers 300 € to B. This is generous and often the most honest solution for a transitional phase.

It is important to put a time limit on this phase and record the date when you will switch back to the percentage formula.

How to check the result every month

The fastest check is the quotient test: contribution ÷ net income must be identical for both individuals and correspond to the value total costs ÷ total net income. In the example: 1,280 ÷ 3,200 = 0.40 and 720 ÷ 1,800 = 0.40, and 2,000 ÷ 5,000 = 0.40. If any value deviates, there is a typo in the table.

Followed by three additional checks:

• Sum test: Both contributions combined equal the household costs exactly. Rounding cents go to the person with the higher share or into the reserve.
• Actual vs. plan: At the end of the month, you compare what was actually spent. Groceries fluctuate, utility bills arrive. You split the difference in the same ratio.
• Out-of-pocket settlement: Whoever pays in the supermarket with their own card creates an open balance. That must land in the ledger, or the split shifts silently.

Familienservice recommends recording joint costs for three months first, then choosing a model and setting the standing order for one to two days after the salary arrives, with roughly a 10% buffer. For 2,000 € in costs, that is a 200 € buffer, split 128 € to 72 €. How to properly settle remaining amounts and out-of-pocket expenses at the end of the month is explained in our article on perfect expense reconciliation with remaining balances.

No spreadsheet chaos means: one number for the standing order, one list for out-of-pocket expenses, one balance. Nothing more.

Frequently asked questions

Is splitting by income unfair to the higher earner?

No, because both give up the same percentage of their income, 40% in the example. The higher-earning person still keeps more in absolute terms: 1,920 € instead of 1,080 €. Whoever earns more continues to benefit from their salary, just not at the expense of the shared home.

Do you calculate with gross or net income?

With net income, meaning the amount that actually hits the account. Gross distorts the ratio because tax classes and deductions differ. For married couples with a III/V combination, it is advisable to balance the net amounts fairly beforehand or calculate both on IV/IV, otherwise the person in class V mathematically pays in too little.

Does the income formula also work in a flat share?

In flat shares, people rarely split by income, but rather by room size and usage, because flatmates do not share a common life plan. The percentage formula can still be applied if you substitute square meters for income. How that looks for rent and utilities is shown in our article on sharing expenses with flatmates.

Is a joint account risky for unmarried couples from a tax perspective?

It can become risky. If one person contributes significantly more to a joint account and the balance belongs equally to both, the tax office can treat the excess as a gift. Unmarried partners have an allowance of 20,000 € within ten years according to Section 16 of the Inheritance Tax Act, while married couples have 500,000 €.

What is the three-account model?

Each person keeps their own current account, supplemented by a joint account exclusively for household expenses. Everyone transfers their proportional contribution to this account via standing order. The advantage: personal expenses remain private, and shared money is clearly demarcated.

Calculate once today, then let it run via standing order

Take ten minutes this evening. Two net salaries, a list of shared costs, the formula. At the end stand two numbers, 1,280 € and 720 € in the example. Those go into the standing order. Done.

What remains afterward are the small things: weekly shopping with your own card, utility back-payments, the hardware store on Saturday. That is precisely what Split The Bill was built for. Snap a photo of the receipt, enter the expense, and the balance shows at any time who owes whom how much. Recurring fixed costs like rent are set up once, and monthly budgets with an email summary show whether the buffer is enough. Everything in the browser, without downloading an app. And the mathematics is deterministic, not an AI estimation.

We have summarized what you should look out for when choosing a tool as a couple in six evaluation criteria for couple expense apps. Calculate first, then decide. No traps.