Loan Interest Calculator
User Guide

The Buildara NZ Loan Interest Calculator is a three-mode finance comparison tool for New Zealand owner-occupiers, property investors and residential developers.

Use it to compare advertised home-loan offers, estimate investment-property cash flow with MBIE area-rent data, or model development-loan drawdowns, fees, capitalised interest and facility headroom.

Results are preliminary estimates, not lending, financial, investment, tax, legal or valuation advice.

Select the mode that matches the decision you are making. The inputs and results change automatically.

• Owner-occupier loans: compare home-loan offers for a purchase or refinance.
• Investment property returns: estimate rental yield, cash flow and finance risk.
• Development finance: model facility use, staged drawdowns, fees and interest.

Enter the purchase price and deposit first. The calculator derives the loan amount, then applies your loan term, repayment frequency, repayment type and comparison period.

• Choose principal-and-interest or interest-only repayments.
• Choose monthly, fortnightly or weekly repayments.
• Use the comparison period to keep every lender offer on the same term.

Add up to four offers. For a selected term, the automatic feed uses each lender's lowest advertised home-loan rate available to the tool. You may replace it with a formal quoted rate.

• Enter lender cashback where applicable; net cost deducts cashback from interest paid.
• A manual rate is clearly labelled and can be restored to the automatic rate.
• Automatic matching excludes renovation, construction, commercial and bridging products.

The results compare estimated repayments, net financing cost, interest paid and remaining balance over the selected comparison period.

The lowest net cost is not always the lowest rate. Cashback, repayment timing and remaining balance can change the ranking.

Enter the property value, loan amount, lender, fixed-rate period, annual rate, loan term and repayment type. Then select the rent source.

• MBIE regional data
• Current tenancy
• Property manager appraisal
• Custom weekly rent

Choose a region, a specific MBIE market-rent area, dwelling type and bedroom count, then load the regional rent result.

MBIE data is an area-level market reference, not a valuation or guaranteed rent for the property. Some combinations have no published result because the sample is unavailable or suppressed.

If no result is available, try another bedroom count, a broader area, or enter a verified rent manually. A no-result response is different from a service connection failure.

Enter expected vacancy, rent growth, rates, insurance, management, maintenance, body-corporate and other annual costs.

Review gross yield, net yield, annual pre-tax cash flow, monthly loan payment, interest cover, break-even rent and break-even rate. Stress checks show the effect of a 1% rate increase and a 10% rent reduction.

Enter the security value, reference LVR, approved facility, initial project proceeds, annual rate, loan period and initial drawdown date.

• Choose monthly cash interest or interest capitalised to maturity.
• Choose whether the interest reserve sits inside the facility or is funded by borrower cash.
• Add lender, legal, broker and other capitalised fees.
• Add staged drawdowns by interest-period number and amount.

Each staged drawdown is treated as occurring at the start of its selected period and accrues interest for that full period. Review total interest, maturity balance, facility utilisation, reserve sufficiency and period-by-period headroom.

Use Save Scenario to store the current inputs in this browser. Use Print / PDF, or the print button inside a result panel, to create a record for discussion.

Saved scenarios use local browser storage. They are not a cloud backup and may be lost if browser data is cleared or another device is used.

The calculator is responsive and works on desktop, tablet and mobile screens. On smaller screens, form sections and results stack vertically for easier review.

• Confirm rates, cashback, fees and eligibility against each lender's formal offer.
• Use a current tenancy or property-manager appraisal when it better represents the specific property than an area median.
• Include realistic vacancy and holding costs rather than relying on gross yield alone.
• Match development drawdown periods to the loan agreement and check whether interest is capitalised or paid in cash.
• Stress-test rates, rent, timing and cost assumptions before making a commitment.

• Public rates may have LVR, salary-crediting, package or other eligibility conditions.
• MBIE rent data represents an area and property category, not the condition or achievable rent of a specific property.
• Development-loan timing, fees, reserve rules and interest calculations must be checked against the executed loan agreement.
• Tax, deductibility, ownership structure and lending suitability are outside this calculator.

The Loan Interest Calculator keeps three related but distinct finance decisions in one bilingual, NZ-focused workspace while preserving separate inputs and results for each mode.