Even, proportional, and what each one equalises
An even split equalises the payment. Both people transfer the same amount, which is simple to run and easy to explain, and it is the arrangement most couples start with. A proportional split equalises the fraction of income left over. Both people end up with the same percentage of their own take-home unspent, which means the higher earner pays more in dollars and neither is squeezed harder relative to what they bring in.
These are two different definitions of fair and there is no third position that satisfies both. When the incomes are close the two produce nearly the same numbers and the choice hardly matters. When one income is double the other, the even split leaves one person with a comfortable surplus and the other with very little, while both technically paid the same. Seeing those two percentages next to each other is usually more useful than any argument about the principle.
The fixed-amount method, and when it fits
Plenty of households do not use a formula at all. One person pays the rent, the other pays everything else, and nobody has calculated whether that comes out even. The third method models exactly that: fixed amounts assigned first, then whatever remains divided in half. It is worth running because it often turns out to sit somewhere between the other two, and occasionally it turns out to be more lopsided than an even split, which is worth knowing if it was chosen because it felt fairer.
If the fixed amounts you enter come to more than the shared total, the arithmetic gives the surplus back evenly and both people pay less than their stated figure. That is usually a sign that the extra is really joint savings, in which case it belongs in the cost list as a line item rather than being buried in a fixed payment.
What is left over is not the same as what is free
The remainder column is before personal spending. Two people left with $1,400 each are not in the same position if one of them has a $600 student loan payment and the other has none. The clean way to handle it is to leave individual debts out of the shared list, where they do not belong, and then subtract each person's own commitments from their remainder before comparing. If you want to see what those individual debts cost over time rather than per month, the debt payoff planner takes them one by one.
Joint savings is the opposite case and does belong in the shared list, if you both fund it. Leaving it out makes both remainders look larger than they are and quietly turns saving into an afterthought funded by whoever happens to have money at the end of the month, which in a two-income household usually means the higher earner accumulates assets faster.
The part the arithmetic cannot reach
Income is one input among several that a household is actually dividing. Hours spent on housework and childcare, whose job the household moved for, who took time out of work and what that did to their earnings afterwards, debts brought into the relationship, and how each person feels about money in the first place are all in the same conversation, and none of them appear anywhere on this page.
What the table is good for is removing one specific failure mode: two people arguing about fairness while working from different numbers. Once both can see that an even split leaves one person with 67 percent of their income and the other with 45, the disagreement becomes about something real, and it is a much shorter conversation.
Questions people ask
Which split is fairest?
They are answers to different questions and neither is objectively right. An even split makes the payment equal, a proportional split makes the leftover fraction equal, and picking one is a decision about which kind of equality you care about. The one useful piece of evidence is the leftover-percentage column: if it shows a large gap under the method you are currently using, that gap is real and it is being felt by one of you, whatever the principle says. Households with large income differences more often land on proportional; households with similar incomes usually find the question does not matter much.
Should joint savings go in the shared cost list?
If you both fund it, yes. Treating savings as a shared expense means it gets split by the same rule as everything else and it gets funded before the remainder is calculated, rather than after. Leaving it out inflates both remainders and tends to mean the person with more left over does more of the saving, which quietly builds assets in one name. If the savings goes into an account in one person's name, that is worth being deliberate about separately.
What about very different incomes, where even is impossible?
The calculator flags it when one person's share exceeds their take-home, because at that point the arrangement cannot be run at all without borrowing. Short of that, the proportional method is what keeps both remainders positive, and it is the reason it exists. In extreme cases even proportional leaves the lower earner with very little in absolute terms, since a percentage of a small income is a small number, and some households handle that by agreeing a floor amount each person keeps before the split is applied.
Do the per-item columns really add up?
Yes, to the cent. Each line is allocated using a running cumulative total rather than by rounding each row independently, so the two columns sum exactly to the same figure as the totals row and there is never a stray cent unaccounted for. That matters if you are using the table as an actual instruction for who pays which bill, since the whole point of the exercise is that nothing quietly falls between the two of you.
Should we use a joint account or transfers from separate ones?
The arithmetic is identical either way, so it is a question of administration and preference rather than fairness. A joint account both pay into makes the shared costs visible to both and removes the monthly reconciliation, but requires agreeing on what counts as shared. Standing orders from separate accounts keep autonomy and are easier to unwind, and require someone to actually check that the shared bills are covered each month. Many households do both: a joint account for the fixed bills and separate accounts for everything else.