Mutual Save & Split
On this page
- The three-step income split formula
- Worked example 1: a moderate income gap
- Worked example 2: a large income gap
- The "equal leftover" alternative
- Which method should you pick?
- Gross or take-home: which number do you use?
- What counts as a "shared" bill?
- A copyable worksheet
- Keeping the split going without the maths
- Frequently asked questions
- Is splitting bills by income fair?
- Should I use gross or net income to split bills?
- How often should we recalculate?
- What if one of us has no income?
- Do we split savings by income too?
- Can this method be used for more than two people?
If you are looking for a splitting bills based on income calculator, you do not actually need special software. The whole method is one percentage and one multiplication, and you can run it on a phone calculator in under two minutes. This guide gives you the three-step formula, two worked examples with real numbers, an alternative "equal leftover" method, and a worksheet you can copy.
Quick answer: divide your take-home pay by the combined take-home pay of both partners to get your share as a percentage, then multiply that percentage by each shared bill. Someone who brings in 60% of the household income pays 60% of the shared costs.
The three-step income split formula
Here is the formula in plain words, with no spreadsheet required.
- Pick one income number and use it for both of you. Use monthly take-home pay (after tax), not the salary on a contract. Take-home is what actually lands in your account, so it reflects what each person can really spend.
- Work out each person's share. Your take-home divided by the two take-home figures added together. Multiply by 100 for a percentage.
- Apply the percentage to every shared bill. Rent, utilities, groceries and internet each get split with the same two percentages.
Written as a formula: your share of a bill = bill amount × (your income ÷ combined income).
Worked example 1: a moderate income gap
Alex takes home $4,200 a month and Sam takes home $2,800. The combined figure is $7,000.
- Alex: 4,200 ÷ 7,000 = 60%
- Sam: 2,800 ÷ 7,000 = 40%
Here are their shared bills for the month.
| Shared bill | Total | Alex (60%) | Sam (40%) |
|---|---|---|---|
| Rent | $1,800 | $1,080 | $720 |
| Utilities | $220 | $132 | $88 |
| Internet | $60 | $36 | $24 |
| Groceries | $600 | $360 | $240 |
| Total | $2,680 | $1,608 | $1,072 |
Compare that with a 50/50 split, where each partner would pay $1,340. Under the income split Sam pays $268 less a month and Alex pays $268 more. In both cases the shared bills take about 38% of each person's take-home pay. That is the point of the method: both partners carry the same proportion of their income.
Worked example 2: a large income gap
The formula holds up when the gap is bigger. Jordan takes home $5,000 and Casey takes home $1,000, a combined $6,000.
- Jordan: 5,000 ÷ 6,000 = 83.3%
- Casey: 1,000 ÷ 6,000 = 16.7%
On $2,400 of shared bills, Jordan pays $2,000 and Casey pays $400. A 50/50 split would ask Casey for $1,200, which is more than Casey's entire take-home pay. If a gap like this describes your situation, see our guide on how to split bills when one partner earns less or has no income.
The "equal leftover" alternative
Some couples prefer a different goal: each person should have the same amount left over after shared bills. The calculation is slightly different.
- Add both take-home figures: $4,200 + $2,800 = $7,000.
- Subtract the shared bills: $7,000 − $2,680 = $4,320.
- Divide what is left by two: $2,160 each.
- Each person pays their income minus $2,160 toward shared bills: Alex pays $2,040 and Sam pays $640.
That is $2,680 in total, and both partners end up with $2,160 for personal spending and savings. It is more generous to the lower earner than the proportional method, so it suits couples with a wide gap or one partner in a lower-earning phase, such as a career change or study. Whichever method you choose, write it down so neither of you has to remember it.
Which method should you pick?
| Method | How it works | Best when |
|---|---|---|
| 50/50 | Each pays half | Incomes are close and bills are modest |
| Proportional to income | Same percentage of income each | Most couples with an income gap |
| Equal leftover | Same money left after shared bills | A large gap, or one partner earning little |
Our article on whether couples should split bills 50/50 goes deeper on when the simple option is still the right one.
Gross or take-home: which number do you use?
Use take-home pay. Gross salary ignores taxes, pension deductions and health insurance, which can differ a lot between two jobs. Using gross can make the split look fair on paper while leaving one partner with much less to spend.
If your pay varies, use an average of the last three to six months, or use your baseline income and revisit the split when it changes. Many couples recalculate once or twice a year, or whenever either of you gets a raise, changes jobs or reduces hours.
What counts as a "shared" bill?
The formula only works if you agree what goes into the pool. A short list that works for most couples:
- Shared: rent or mortgage, utilities, internet, household groceries, home insurance, shared subscriptions.
- Personal: clothes, hobbies, individual phone plans, personal subscriptions, gifts for your own family.
- Case by case: dining out together, holidays, pets, cars. Agree on these in advance rather than arguing bill by bill.
Our guides on splitting rent as a couple and splitting utility bills show how to treat the biggest items.
A copyable worksheet
Copy this into a note or spreadsheet and fill it in once a year.
| Line | You | Partner | Combined |
|---|---|---|---|
| Monthly take-home pay | ___ | ___ | ___ |
| Share of combined income (%) | ___ | ___ | 100% |
| Shared bills this month | ___ | ||
| Amount you each pay | ___ | ___ | ___ |
Keeping the split going without the maths
The formula is simple, but applying it to every grocery run is where couples give up. Our app, Mutual, supports income-based splitting alongside shared expense tracking, monthly budgeting, savings goals, bill reminders and reports for two people. It is available on the App Store for iPhone. If you track by hand instead, a monthly settle-up works well; our guide to tracking shared expenses as a couple shows a light-touch system.
Frequently asked questions
Is splitting bills by income fair?
It is fair to many couples because each partner contributes the same share of their income, so neither feels squeezed. Fairness is personal, though, so agree on the method together instead of assuming one is correct. Our article on splitting bills fairly when you earn different amounts covers the pros and cons.
Should I use gross or net income to split bills?
Use net (take-home) income. It reflects what each person can actually spend after taxes and deductions.
How often should we recalculate?
At least once a year, and any time either income changes by a meaningful amount. Put a reminder in your calendar for your monthly or annual money check-in.
What if one of us has no income?
A strict percentage would make the non-earning partner's share zero, which can work if you both agree. The equal leftover method or a fixed small contribution are alternatives. Talk through what feels respectful to both of you.
Do we split savings by income too?
You can. Many couples contribute to a shared savings goal using the same percentages so progress stays fair. Others choose equal amounts for savings and income-based shares for bills. The key is to decide in advance.
Can this method be used for more than two people?
Yes. Add every person's take-home pay to get the combined total, then divide each person's income by that total.
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