Split Loan Optimiser Calculator NZ 2026/27
A split loan, also called a split mortgage, divides your home loan into two or more separate portions, each carrying its own interest rate and term, instead of committing the entire balance to a single fixed or floating rate. This calculator models up to three portions, for example part on a 1-year fixed rate, part on a 2-year fixed rate, and the remainder floating, and shows the blended interest rate across the whole loan, the combined monthly and weekly repayment, and the share of your borrowing sitting on a floating rate. Enter the dollar amount, interest rate and term for each portion you are considering, along with your overall loan term, and the results update instantly as you type. The blended rate is the amount-weighted average of your portions, the figure most borrowers compare against a single fixed-rate offer from a bank. This is useful for anyone deciding how to structure a refix, weighing the certainty of a fixed rate against the flexibility of floating, or sanity-checking a split a bank or adviser has proposed. Figures are indicative only; confirm the actual structure, current rates and any restructuring cost with your own bank or a mortgage adviser.
Repayment basis: each portion is amortised separately as a standard table (principal and interest) loan over the loan term you enter, using the standard annuity formula, then the portions are added together. This mirrors how a bank actually schedules a split loan and can differ very slightly from a single loan calculated at the blended rate.
Interest rates: there is no single official "split loan rate" in New Zealand; fixed and floating rates are set individually by each bank and move with wholesale and Official Cash Rate conditions. The default rates shown are illustrative placeholders only, replace them with the actual rates you have been quoted.
Portion limits and fees: the number of portions allowed, minimum portion size and any restructuring fee are set by each bank individually and are not a matter of NZ law; confirm these with your own lender.
Last verified: July 2026, against current Reserve Bank of New Zealand monetary policy context and standard NZ bank split-loan practice.
Source data: Reserve Bank of New Zealand and Commerce Commission, lender responsibilities under the CCCFA.
| Portion | Term | Amount | Rate | Monthly repayment |
|---|---|---|---|---|
| 1 | $0 | 0% | $0 | |
| 2 | $0 | 0% | $0 | |
| 3 | $0 | 0% | $0 | |
| Total | $0 | |||
What Is a Split Loan?
A split loan divides your total home loan balance into two or more separate portions, each with its own interest rate, term and structure. Rather than putting the entire balance on one fixed rate or leaving it all floating, you might fix part for a year, part for two years, and leave the remainder floating. Each portion behaves like its own small loan, with its own maturity date and, if fixed, its own break fee for early repayment. The portions sit on the same mortgage but are tracked and repriced independently.
How the Blended Rate Is Calculated
The blended rate is the amount-weighted average of each portion's rate: multiply each portion's balance by its rate, add the results together, then divide by the total loan amount. A larger portion pulls the blended rate toward its own rate more strongly than a smaller portion does. This is the figure most borrowers use to compare a split structure against a single fixed-rate offer, and it is the headline result this calculator displays.
Why Split Instead of Choosing One Rate?
Fixing the whole loan gives certainty but little flexibility: extra repayments can trigger a break fee, and a rate fall leaves you stuck at the higher fixed rate. Floating gives full flexibility, including free extra repayments, but every repayment moves when your bank's floating rate changes, which broadly tracks the Official Cash Rate. Splitting holds both positions at once, with risk spread across more than one rollover date rather than a single day.
Rollover Risk and Staggering Terms
Each fixed portion matures and rolls over onto a new rate, set at whatever the market offers that day. A single fixed term reprices the whole balance at once; splitting into portions with different terms staggers these dates, so only part of the loan is exposed at any one time. This calculator flags when two or more fixed portions share the same term, since identical terms will still roll over together, giving no staggering benefit.
Worked Example
Consider a $600,000 mortgage split three ways: Portion 1 is $200,000 on a 1-year fixed rate of 5.75%, Portion 2 is $250,000 on a 2-year fixed rate of 5.55%, and Portion 3 is $150,000 floating at 7.35%. The blended rate is (200,000 × 5.75% + 250,000 × 5.55% + 150,000 × 7.35%) ÷ 600,000 = 6.07%. Amortised separately over 30 years, the portions cost about $1,167.15, $1,427.33 and $1,033.46 a month, a combined total of roughly $3,627.93 a month, or $837.21 a week. A single $600,000 loan calculated directly at 6.07% over 30 years works out to about $3,623.06 a month, a few dollars lower, since summing three separately amortised portions is not mathematically identical to amortising one balance at the average rate. Here, 25% of the loan is floating, and because Portions 1 and 2 have different terms, they roll over on different dates.
Who This Calculator Is For
This calculator is for anyone structuring a mortgage refix or new home loan across more than one rate, borrowers comparing a bank or adviser's proposed split against the numbers themselves, and anyone checking how much of their loan is exposed to floating-rate movements versus locked in for certainty, or whether a proposed split actually staggers rollover risk.
What This Calculator Assumes
- Each portion is a standard table (principal and interest) loan, amortised over the loan term you enter.
- The blended rate is the amount-weighted average of the portions entered; it is not a rate a bank publishes or guarantees.
- There is no fixed "split loan rate" in New Zealand; the default rates shown are illustrative placeholders, not current market rates, and should be replaced with figures actually quoted to you.
- No allowance is made for break fees on restructuring an existing fixed portion, or for any bank fee to set up additional portions.
- The number of portions a bank allows and any minimum portion size are set by each lender, not by law, and are not modelled here.
- Results are indicative only and are not a lending decision or financial advice. Confirm your structure with your bank or a mortgage adviser.
Frequently Asked Questions
What is a split home loan?
A split home loan divides your mortgage into two or more portions, each with its own rate, term and structure, instead of one fixed or floating rate for the whole balance. A common example: part on a 1-year fixed rate, part on a 2-year fixed rate, and the remainder floating.
How do you calculate the blended interest rate on a split loan?
Multiply each portion's balance by its interest rate, add the results together, then divide by the total loan amount. A larger portion has more influence on the blended rate than a smaller one at the same rate.
How many portions can I split a mortgage into?
Most New Zealand banks allow several portions, commonly up to around five, though the exact number, minimum portion size and any restructuring fee vary by lender. Check your own bank's current lending criteria before assuming a particular limit.
What is floating-rate exposure and why does it matter?
It is the percentage of your loan on a floating rate rather than fixed. A higher floating percentage means more of your repayment moves immediately when your bank's floating rate changes, but also more of your loan can be repaid early without a break fee.
Why doesn't my repayment total exactly match a single loan at the blended rate?
Each portion amortises separately as its own smaller loan, then the repayments are added together, which is not mathematically identical to calculating one repayment on the full balance at the blended rate. The difference is normally only a few dollars a month.
What happens when one portion of a split loan reaches the end of its fixed term?
That portion rolls over onto a new rate and term you choose, while your other portions continue undisturbed. Only the matured portion is exposed to rates on that day, which is why staggering fixed terms matters. Our Fixed Term Expiry Planner works out the rollover date and new repayment for a single fixed term.
Is a split loan the same as a revolving credit or offset mortgage?
No. A split loan divides your balance across different rates and terms to manage rate risk. A revolving credit or offset facility is a floating structure where surplus cash in a linked account reduces the interest charged. Many borrowers use both together. See our Revolving Credit Calculator.
Does splitting an existing mortgage cost anything?
Splitting at the time you first draw down or refix a portion generally costs nothing extra. Restructuring an existing fixed portion partway through its term can trigger a break fee, based on the gap between your fixed rate and current wholesale rates. Ask your bank or adviser for the actual cost first.
Related Mortgage Calculators
- Bank Test Rate Calculator: see how much smaller your approved loan can be once a bank tests it at its higher servicing rate.
- Fixed Term Expiry Planner: work out the rollover date and new repayment when a fixed portion matures.
- Mortgage Refinance Calculator: check whether switching lenders or rates is worth it after fees and any cashback.
- Revolving Credit Calculator: model a floating portion structured as revolving credit against surplus income.
- Mortgage Calculator: a straightforward single-rate repayment calculator for the whole loan.
Official NZ sources
This calculator is built from primary New Zealand sources. Always confirm current figures against the official source for your situation:
- Reserve Bank of New Zealand: Official Cash Rate and current monetary policy
- Commerce Commission: lender responsible lending obligations under the CCCFA
- Reserve Bank of New Zealand: understanding debt-to-income restrictions on mortgage lending
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