Enter the average daily balance kept in your linked accounts. The calculator will automatically apply this cash to reduce the interest charged on your eligible splits above.
📈 The Ultimate NZ Mortgage Structuring Calculator
Whether you are buying your first property or restructuring an existing property portfolio, finding the right home loan setup is the difference between decades of debt and financial freedom.
We built the Home Loan Factory Mortgage Calculator to give everyday Kiwis access to the exact same math the banks use. From standard Principal & Interest (P&I) loans to complex split structures featuring Revolving Credit and Offset accounts—you can build it here.
How to use this calculator
1. The Simple Setup (For quick estimates)
Choose your goal: Select either "Buying a Property" or "Already Own My Home".
Enter the basics: Drop in your purchase price and deposit (or total loan balance), your term, and current interest rate.
See your costs: The calculator will instantly show your required repayments. Use the "Rates & Insurance Tool" to get a true picture of your actual weekly household costs.
Pay it off faster: Slide the "Increased Repayment" tracker to instantly see how much interest you can save, and exactly how many years you can slash off your loan term by paying a little extra.
2. The Advanced Setup (For split loans and smart structuring)
Are you mixing fixed rates with floating? Using an offset account? Click the Advanced (Split Loans) button to unlock professional-grade structuring:
Click "+ Add Loan Split" to break your total loan into multiple chunks (e.g., $400k Fixed, $100k Revolving Credit).
Assign specific interest rates, repayment types (P&I, Interest-Only, Revolving Credit, or Offset), and varying loan terms to each individual split.
Once your splits match your total loan amount, the calculator will blend them into a single, easy-to-read "Combined Repayment."
Pro Tip: Export Your Plan
Once you've built your perfect structure, click "Copy Loan Chart." This instantly copies a beautifully formatted table of your exact loan splits directly to your clipboard. You can paste it straight into an email to us, or save it to your own notes!
Frequently Asked Questions (Home Loan Structuring)
How do I pay off my mortgage faster? One of the most effective ways to pay off a mortgage faster is by making extra principal payments above your bank's minimum requirement. Even an extra $50 a week can shave years off your loan. If you have a "Split Loan", you can use the Avalanche Method: direct all of your extra cash toward the loan split with the highest interest rate first, while paying the minimums on the rest. Our calculator does this math for you automatically!
What is the difference between Revolving Credit and an Offset Mortgage? Both are designed to reduce the amount of interest you pay, but they work differently:
Revolving Credit: This acts like a giant overdraft on your transaction account. Your income goes straight into the loan, reducing the balance and the interest calculated daily. You can dip back into the funds up to your limit as needed.
Offset Mortgage: Your loan and your savings remain in separate accounts, but the bank "offsets" your savings against your loan balance before calculating interest. If you have a $100,000 loan and $20,000 in a linked savings account, you only pay interest on $80,000.
Can I make extra repayments on an Interest-Only loan? Generally, banks do not allow you to make extra principal payments during an active Interest-Only (IO) period. If you have extra cash to apply, you must either direct it toward a standard Principal & Interest (P&I) loan split, or put it into a savings/offset account to prepare for when your IO period ends.
Are local council rates and house insurance included in my mortgage? No, your bank repayment only covers your loan principal and interest. However, council rates and house insurance are mandatory ongoing costs of property ownership in New Zealand. Our calculator includes a Rates & Insurance Estimate Tool so you can see the "True Cost" of your housing commitment, preventing you from over-stretching your household budget.
About this calculator
The Home Loan Factory Mortgage Calculator is a professional-grade financial tool designed specifically for New Zealand homebuyers, current homeowners, and property investors.
Unlike basic bank calculators that only show generic minimum repayments, our tool allows you to build, visualize, and test comprehensive home loan structures—including true-cost budgeting, complex split loans, revolving credit facilities, and intelligent debt-reduction strategies.
Core Capabilities & Features
Intelligent Scenario Toggling: Seamlessly switch between "Buying a Property" and "Already Own My Home." The calculator intuitively converts your purchase price and deposit into a standalone loan balance for quick refinancing or top-up comparisons.
"True Cost" Household Budgeting: A mortgage isn't your only expense. Users can toggle on the Rates & Insurance Tool to automatically embed estimated local council rates and house insurance into their regular cash flow. This provides a highly realistic view of your actual housing costs.
Professional Loan Splitting (Advanced Mode): Don't settle for a single interest rate. Open the Advanced tab to split your mortgage into multiple tranches. You can assign completely independent interest rates, loan terms, and repayment frequencies to each split to build the perfect mix of fixed and floating debt.
Advanced Product Types: Model how different bank products interact. The calculator accurately handles standard Principal & Interest (P&I) alongside Interest-Only (IO) phases. It also fully supports advanced NZ bank products like Revolving Credit, Revolving Credit (Reducing), and Offset accounts.
Interest-Only Phase Mapping: If you select an Interest-Only term, the calculator dynamically splits your timeline. It accurately displays your Phase 1 (Interest-Only) payments, and explicitly calculates the Phase 2 "payment shock" when your loan reverts to Principal & Interest for the remaining term.
"Smart Payoff" Debt Avalanche Engine: Our interactive "Pay It Off Faster" slider isn't just doing basic math. If you have a split loan, the calculator uses the "Avalanche Method." It automatically detects your highest-interest P&I split and optimally targets your extra cash there first. It also intelligently knows to hold back extra payments from Interest-Only or Offset splits until their fixed periods end.
Instant Amortization Visualizer: Every change you make updates a dual-line graph instantly, allowing you to visually compare a standard 30-year payoff against your accelerated "Smart Payoff" timeline.
One-Click Proposal Exporting: Built the perfect structure? Use the "Copy Link" button to generate a custom URL that saves your exact parameters to share with a partner or adviser. Alternatively, click "Copy Loan Chart" to instantly copy a perfectly formatted, professional HTML table of your loan splits directly to your clipboard, ready to paste into an email or Word document.