Why Your Borrowing Power Is Lower Than You Think

There's a moment in almost every first-home buyer's journey where the bank tells them a number and it's significantly lower than what they expected. It's deflating. Sometimes it's devastating — especially if you've already found a property and made plans around a budget that doesn't exist.

The gap between what you think you can borrow and what the bank will actually lend you typically comes down to four things.

1. The stress-test rate

Banks in New Zealand don't assess your ability to repay at the rate you'll actually pay. They use a stress-test rate — currently 7% — to make sure you could still afford repayments if rates rose significantly.

This is a sensible safeguard, but it has a big impact on your numbers. If actual rates are 6%, being assessed at 7% reduces your borrowing power by roughly 8–10%. If actual rates are 5.5%, the reduction is even larger.

Most online mortgage calculators use the actual rate, not the stress-test rate. So when you plug in 6% and get a number, you're seeing a figure that's meaningfully higher than what the bank will approve. The disappointment is built into the tool.

2. Net income isn't what you think

When people think about their income, they usually think about their gross salary. But banks lend based on what's left after:

• PAYE tax — progressive rates from 10.5% to 39%
• ACC earners' levy — currently 1.60% on earnings up to $142,283
• KiwiSaver contributions — 3%, 4%, 6%, 8%, or 10% of gross pay
• Student loan repayments — 12% on income above the $22,828 threshold

A single earner on $85,000 gross might assume they take home around $65,000. The actual figure — after PAYE ($16,582), ACC ($1,360), 3% KiwiSaver ($2,550), and student loan ($7,461) — is closer to $57,047. That's $8,000 less than the rough estimate, and it directly reduces borrowing power.

For a household with two earners, KiwiSaver rates, and student loans, the gap between perceived and actual net income compounds further.

3. Expenses count more than you expect

Banks assess your living expenses carefully. They'll compare what you declare against their own benchmarks and use whichever is higher. If you declare low expenses but your bank statements show regular Uber Eats, subscription services, and weekend spending, the bank will use the higher figure.

Common expenses that surprise borrowers:

• Childcare: $200–$400/week per child significantly reduces your available income
• Insurance: Health, life, car, contents — these add up to $200–$400/month for many households
• Transport: Car payments, fuel, registration, WOF — banks count all of it
• Subscriptions: Netflix, Spotify, gym, phone plans — individually small, collectively material

The gap between what you think you spend and what you actually spend is almost always larger than you expect. And every dollar of expenses reduces the amount available for mortgage repayments.

4. The DTI ceiling

Even if your income could comfortably service a large loan, the RBNZ's debt-to-income restrictions create an absolute ceiling. For owner-occupiers, total debt (including the new mortgage) generally can't exceed 6× gross household income.

On a household income of $130,000, the DTI cap is $780,000. If you have $25,000 in existing debt (car loan, credit card limits, personal loan), your maximum mortgage drops to $755,000 — regardless of how comfortably you could service more.

The DTI cap often binds before the serviceability test does, especially for higher-income households with moderate expenses. It's the ceiling you don't see coming.

Closing the gap

The solution isn't complicated — it's just about knowing the real numbers before you start.

1. Calculate your actual net income — not a rough estimate, but the real figure after PAYE, ACC, KiwiSaver, and student loan. Use NZ-specific tax rules, not a generic percentage.
2. Map your real expenses — go through three months of bank statements and categorise everything. The number will be higher than you think, and that's exactly the number the bank will use.
3. Assess at the stress-test rate — any borrowing estimate that uses the actual interest rate is misleading. Use 7% to see what the bank will actually approve.
4. Check your DTI — add up all existing debts, multiply your gross income by 6, and see how much room you have for a mortgage.

How MortgageReady does this for you

MortgageReady runs all four of these calculations automatically using current NZ rules. You enter your gross income, KiwiSaver rate, and student loan status — and it calculates your exact net income using the correct PAYE brackets, ACC levy, and deduction rates.

It then factors in your actual expenses and existing debts to show four borrowing scenarios — conservative (40% surplus buffer), comfortable (25% buffer), optimistic (10% buffer), and your target property — all assessed at the stress-test rate and capped by the DTI limit.

The result is a set of numbers that closely matches what a bank or broker will tell you. No surprises, no disappointment — just clarity before the conversation starts.

See your real borrowing power — it takes under five minutes, and it might save you from a number you weren't expecting.