Most backyard builds are funded with a mortgage top-up against existing equity. At the calculator’s defaults (5.9% over 25 years), borrowing the $166,000 turnkey cost of a Kōwhai 60 runs about $244 a week. A new two-bed typically rents for $500 to $800. That gap is the arithmetic this page exists to show (indicatively, not as lending advice).
Slide the numbers and see the weekly cost of borrowing for the build. Set against typical rent, most owners find the maths does the convincing.
Indicative only, not lending advice. Your bank sets the real rate and terms. Rent figure is the typical $600/wk for a two-bed minor dwelling in regional NZ.
Borrowing the full turnkey cost of each footprint at 5.9% over 25 years: no deposit, the straight arithmetic. Slide your own rate, term and deposit in the tool above.
| BUILD | WEEKLY | MONTHLY | TOTAL INTEREST OVER TERM |
|---|---|---|---|
| Fern 48 · borrow $133,000 | $196/wk | $849/mo | $121,643 |
| Kōwhai 60 · borrow $166,000 | $244/wk | $1,059/mo | $151,825 |
| Rātā 70 · borrow $194,000 | $286/wk | $1,238/mo | $177,434 |
Standard table amortisation, computed with the same formula as the calculator. Your bank sets the real rate, term and structure. Treat these as planning numbers, not an offer.
The column that decides most projects: typical two-bed rent in each area minus the $244/wk repayment on a Kōwhai 60 borrowed in full.
| AREA | TYPICAL TWO-BED RENT | KŌWHAI 60 REPAYMENT | WEEKLY MARGIN |
|---|---|---|---|
| Queenstown | $800/wk | $244/wk | $556/wk |
| Auckland | $750/wk | $244/wk | $506/wk |
| Wānaka | $750/wk | $244/wk | $506/wk |
| Wellington | $700/wk | $244/wk | $456/wk |
| Tauranga | $650/wk | $244/wk | $406/wk |
| Hamilton | $620/wk | $244/wk | $376/wk |
| Christchurch | $620/wk | $244/wk | $376/wk |
| Napier & Hastings | $600/wk | $244/wk | $356/wk |
Rents are indicative planning figures for a warm, compliant two-bed minor dwelling. Verify against Tenancy Services bond data for your suburb. Gross margin before rates, insurance, maintenance and vacancy.
Not advice, just the three shapes that come up on nearly every feasibility call.
Lending rules, rates and tax treatment change and differ by person. Confirm anything that matters with your bank, broker or accountant before committing.
Three shapes come up again and again: a top-up on the existing mortgage against the equity in the main house, construction lending drawn down in stages against the fixed quote, and a mix of savings plus a smaller top-up. Which fits you is a conversation for your bank or adviser. The tool here shows what any of them costs per week at your numbers.
At the tool's defaults, borrowing the full turnkey cost of any Seventy runs $196 to $286 a week, while a new two-bed minor dwelling typically rents for $500 to $800 depending on the region. Gross rent isn't profit (rates, insurance, maintenance and vacancy come out of it), but the gap is why so many builds are rental-led.
Most owners borrow against equity in the property the flat is built on rather than saving a separate deposit. How much a bank will lend depends on your equity position, income and their current lending rules; the deposit slider in the tool shows how much any given contribution changes the weekly number.
Lenders want certainty: a fixed-price quote, signed plans from a recognised professional, and evidence the build is lawful. A Seventy set is built for that conversation: architect-signed drawings, the consent-exemption paperwork completed for your address, and a fixed turnkey quote if we build it.
That's between you and your lender. Rates, terms and break costs change constantly, and this page doesn't give financial advice. The calculator models any rate from 4% to 9%, so you can stress-test the weekly number against a higher rate before you commit to anything.
A permanent, compliant second dwelling adds rentable floor area on the title you already own, and it is treated as real housing stock by tenants and valuers alike, unlike a sleepout or cabin. How much value it adds varies by region and market; the dependable part is the weekly rent it earns while you hold.
Free site check · fixed quote · plans your bank recognises.