Joint Mortgage Split Calculator NZ

This calculator works out how to split a shared mortgage repayment fairly between two people, whether you are a couple, siblings or flatmates who own a home together. A straight 50/50 split can put more strain on the lower earner, so many people prefer splitting in proportion to income instead, where each person contributes the same percentage of their pay rather than the same dollar amount. You enter the total repayment for the period, weekly, fortnightly or monthly, plus each person's income. The calculator then shows two results side by side: an income-based split giving the exact amount Person A and Person B would each pay under a proportional arrangement, and a simple equal split for comparison. Seeing both figures together makes it easy to agree on an approach that feels fair, especially where one partner earns considerably more than the other. Use it when setting up a joint mortgage for the first time, revisiting an arrangement after a change in income, or when you just want a clear starting point for a money conversation. Remember that how you split repayments is separate from legal ownership of the property; if contributions differ from a 50/50 ownership share, it is worth recording the arrangement in writing and getting independent legal advice. The figures given are indicative only, meant to support a fair conversation rather than replace professional financial or legal advice.

Advertise on this page

Total repayment (per period)

Person A income

Person B income

$923 / $677

income-based split (A / B) per period

Person A (by income)$923

Person B (by income)$677

Equal split each$800

The income-based split has each person pay the same proportion of their pay; the equal split divides the repayment in half. How you split repayments is separate from legal ownership; consider a property-sharing agreement and legal advice. Estimate only.

How it works

The calculator works out each person's share of the combined income, then applies that share to the repayment for the income-based split, so the higher earner pays more but each pays the same percentage of their pay. It also shows a simple 50/50 split for comparison. Seeing both side by side helps a couple or flatmates agree a split that feels fair to everyone.

Worked example

On a $1,600 repayment with incomes of $75,000 and $55,000, the income-based split is about $923 for Person A and $677 for Person B, versus $800 each on an equal split. The income-based split leaves each with the same proportion of pay.

Related calculators

Mortgage Repayment Calculator: the repayment.
Flatmate Rent Split Calculator: split rent.
Second Income Budget Calculator: combined budget.
Borrowing Capacity Calculator: what you can borrow.

Frequently asked questions

How should a couple split mortgage repayments?

Some couples split 50/50, others split in proportion to their incomes so the repayment is an equal share of each person's pay. There is no single right way; the fairest split is the one you both agree on, which this calculator helps you set out clearly.

Why split by income?

Splitting by income means each person contributes the same proportion of their pay, which can feel fairer where incomes differ a lot. A 50/50 split is simpler but takes a bigger bite out of the lower earner's pay.

Does the split affect ownership?

How you split repayments is separate from legal ownership shares. If contributions differ, it is worth recording the arrangement, and getting legal advice on ownership and a property-sharing agreement.