Enter both monthly incomes, the shared expenses you have agreed to divide, and each person's essential costs outside that shared total. The calculator shows a 50/50 split, an income-based split, and an optional split of your own. For each method, it shows usable money or an explicit shortfall after the entered essentials.

The calculator keeps the figures only in your browser tab. Nothing is saved or sent, and it asks for no names, account details, or email address.

Get the five inputs right

Use income that is actually available for the same month. For weekly, fortnightly, or irregular pay, convert both incomes to one monthly planning figure. The couples budget calculator can normalize several payment frequencies.

The shared-expense total should contain only costs covered by this agreement. Do not quietly put one person's private cost into the shared column or leave a household cost out because someone currently pays it.

If you have not decided which costs are shared, start with the guide to splitting finances as a couple before entering a total.

Looking back over several months can prevent less frequent household costs from disappearing from the shared-expense estimate. That is the method used in the CFPB's spending assessment.

Decide whether you are entering gross income, take-home income, or another consistent figure. Take-home income is often easier for a household cash-flow comparison, but the useful rule is simpler: use the same basis for both people and write down what you chose.

Enter each person's essential costs outside the shared total separately. This is where an individual transport pass, medicine, required debt payment, or support obligation belongs if it is not in the shared number. Do not add optional personal spending here just to make a preferred split look impossible.

The form deliberately takes one shared-expense total instead of rebuilding a household budget. Our couples budget calculator already builds that total with bill rows and frequency conversion. Keeping those rows there lets this tool compare contribution rules without duplicating a second budget editor.

What each split calculates

The equal split divides shared expenses in half. If a half-cent remains after rounding, Partner A receives the extra cent.

The income-based split uses these formulas:

Partner A income share = Partner A income ÷ combined income

Partner A contribution = shared expenses × Partner A income share

Partner B's contribution is the rest of the shared expenses after Partner A's contribution is rounded to two decimal places. This makes the two displayed contributions add back to the entered total.

For each partner, the calculator then uses:

usable remainder = income - shared contribution - essential costs outside the shared total

shortfall = max(0, -usable remainder)

The custom comparison accepts any two non-negative contributions that add up to the shared expenses. It is useful when a strict income ratio misses something important, such as personal debt payments, care costs, an irregular income floor, or an agreed adjustment for unpaid work.

The calculator reports each partner's usable remainder and any shortfall after the shared contribution and entered outside essentials. It still treats equal, income-based, and custom contributions as comparisons, not verdicts about fairness.

Once the contribution method is clear, joint and separate account systems can help you decide how the money will move in practice.

Worked example: the same bills, three different effects

Alex has monthly income of 3,200 and 800 of essential costs outside the shared total. Rui has income of 1,800 and 500 of outside essentials. They plan to share 3,000 in expenses.

                                  Alex       Rui
Equal contribution              1,500     1,500
Usable remainder                  900      -200
Shortfall                           0       200

Income-based share                 64%       36%
Contribution                     1,920     1,080
Usable remainder                  480       220
Shortfall                           0         0

Custom contribution              1,700     1,300
Usable remainder                  700         0
Shortfall                           0         0

Alex earns 64% of the combined income (3,200 ÷ 5,000), so this method assigns Alex 1,920 and Rui 1,080.

A half-and-half split leaves Rui 200 short once the entered essentials are paid. The income-based split leaves 480 for Alex and 220 for Rui. The custom split leaves 700 and 0. None is automatically right. The screen now makes the consequence impossible to hide behind a tidy percentage.

Check the result from both seats

Each partner should answer separately before choosing a split:

  • What essential or personal costs still come out of my remaining income?
  • Is my income stable enough for this contribution every month?
  • Will I still have usable money of my own?
  • What household work or care is missing from the income figures?
  • What event should trigger a recalculation?

The ILO's major report on care work treats unpaid care as work with economic and social value. It does not give households a price or bill-split formula. It does rule out treating wages as the only contribution worth discussing.

Try the split for one or two pay cycles and review the effect, not only the formula. A plan that is tidy on screen can still leave one person unable to replace shoes, see friends, cover medicine, or absorb a small surprise.

What this calculator leaves out

It does not calculate tax, benefits, currency conversion, debt liability, ownership, unpaid work, changing income, or the legal effect of paying a bill. Usable remainder includes only the outside essentials entered. It does not mean spare money.