Mortgage Calculator NZ – Weekly, Fortnightly and Monthly Repayments

The shape of a 30-year loan

Each bar is the balance left at the end of that year. A mortgage melts slowly at first — in year 1 of the default loan, NZ$38,802.54 of what you pay is interest and only NZ$6,706.35 comes off the balance — then faster and faster as the principal share grows.

Keep going on the same numbers

Repayments are only the start — these tools cover paying the loan off early, switching it, and the Canadian cousin of this calculator.

How it works

Three steps between a loan amount and the number that leaves your account.

The math behind the default loan

Year by year: the default loan, paid monthly

Interest charged each year, principal repaid each year, and the balance still owing at each year end, for NZ$600,000 at 6.5% over 30 years with no extra repayments. Change the inputs above and this table rebuilds itself.

Two things worth understanding before you sign

The fortnightly myth, and the menu of loan types a New Zealand lender will put in front of you.

The first year versus the last year

The repayment never changes, but what it buys changes completely. The page’s own year-by-year table for NZ$600,000 at 6.5% over 30 years shows the shift.

In year one, interest is NZ$38,802.54 and principal is NZ$6,706.35, from twelve payments totalling NZ$45,508.89, leaving a balance of NZ$593,293.65. Only about one dollar in seven of the first year’s payments reduces the loan; the rest pays for the use of the money. In year ten, interest is NZ$33,490.04 and principal is NZ$12,018.85, leaving NZ$508,656.76. The principal share has nearly doubled, but interest still dominates. The crossover, where principal first exceeds interest in a year, does not arrive until well past the halfway mark of the loan, because the balance stays large for so long.

In year twenty, interest is NZ$22,526.64 and principal is NZ$22,982.26, leaving NZ$333,991.70: the year the principal share finally edges ahead. In year thirty, the last year, interest is only NZ$1,562.60 and principal is NZ$43,946.30, clearing the loan to zero. The whole loan costs NZ$765,266.93 of interest on NZ$600,000 borrowed, more than the amount borrowed, and most of that interest is paid in the first half of the loan. That front-loading is not a penalty or a fee. It is the arithmetic of charging interest on a large balance: the first payments are mostly interest because the balance is at its largest, and the principal share grows only as the balance shrinks.

The practical consequence is about timing. Extra repayments made early attack the balance when it is largest, and therefore save the most interest, because every dollar of principal removed early stops charging interest in every year that follows. Extra repayments made late, when the balance is small and the payments are mostly principal anyway, save far less. The next section puts a figure on that difference.

NZ$200 extra a month: four years and NZ$121,989.57

The most persuasive number on this page is not the repayment. It is what a modest extra payment does to the whole loan, and this calculator shows it directly.

With no extra repayments, the default loan costs NZ$765,266.93 of interest over 30 years and 360 payments. Add NZ$200 a month, making the repayment NZ$3,992.41 instead of NZ$3,792.41, and total interest falls to NZ$643,277.36, a saving of NZ$121,989.57, and the loan ends in 26 years and 312 payments, four years early. The extra payments total NZ$62,400 over the shortened term, 312 payments of NZ$200, and they save nearly twice that amount in interest, because each extra dollar removes principal that would otherwise have charged interest for years.

The comparison that matters is not extra repayments versus no extra repayments in the abstract. It is extra repayments versus the other uses of NZ$200 a month, and the answer depends on the rate on those other uses. Money earning less than 6.5% elsewhere is worse off there than in the mortgage, because the mortgage return is the interest avoided, at 6.5%, with no tax or risk adjustment in this simple comparison. Money needed for an emergency fund, or earning more than 6.5% with acceptable risk, is a different case, and the calculator does not decide it. What the calculator does decide is the size of the prize: NZ$121,989.57 of interest and four years, for NZ$200 a month, on this loan. Any alternative use of the money should be judged against that figure, not against the monthly repayment.

One caution belongs here. Extra repayments help only if they actually reduce the principal, which depends on the loan’s terms: some fixed-rate loans limit extra repayments, or charge a break fee for paying down faster than the schedule allows. Check the loan documents before committing to an extra payment, and confirm with the lender that the extra amount is applied to principal rather than held as a prepayment of future instalments. An extra payment that merely advances the next due date, without shrinking the balance, saves no interest at all.

Three ways to pay, and the fortnightly trap

Monthly, fortnightly and weekly are not three prices for the same loan. Two of them are the same loan divided differently, and the third is a different loan in disguise.

The calculator shows the same loan three ways. Monthly, the repayment is NZ$3,792.41. Weekly, it is NZ$874.58. A true fortnightly repayment, the loan simply spread over 26 payments a year, is NZ$1,749.52, and it saves only NZ$643.35 of interest against paying monthly, because payments land a little sooner. Those three figures are the same total paid in different slices, and the interest differences between them are small, because the same amount is paid each year.

The fortnightly trick is different, and it is the figure to check carefully on any lender’s paperwork. If the monthly repayment is halved and that half is paid every fortnight, the borrower makes 26 half-payments a year, the equivalent of 13 monthly payments, not 12. That thirteenth payment is pure extra principal, every year, which is why loans paid this way finish years early. The trap is that the two fortnightly figures look almost identical, NZ$1,749.52 for the true fortnightly repayment and NZ$1,896.21 for the halved monthly repayment, but one finishes on schedule and the other finishes early, because only the second pays extra. Before signing, check which figure is on the paperwork, and check that the payment matches the schedule that was agreed, not merely the frequency label.

Deposit, loan size, and the rate you should enter

Three inputs, three different kinds of error, and the calculator is only as honest as the figures entered into it.

The deposit sets the loan, and the loan sets everything else. On a NZ$750,000 price with a NZ$150,000 deposit, the loan is NZ$600,000, the default on this page. A smaller deposit means a larger loan at the same rate, and therefore a larger repayment and far more total interest, because interest is charged on the larger balance for the whole term. A larger deposit does the reverse, and the saving from a larger deposit is larger than the deposit itself, because the deposit also avoids the interest that would have been charged on it. The deposit is therefore the highest-leverage input on the page: every extra dollar of deposit saves more than a dollar over the life of the loan.

The rate deserves equal care. The calculator divides the yearly rate by the number of payments per year, so a 6.5% yearly rate paid monthly is 0.5417% a month, and the repayment follows from that period rate. Enter the rate the lender actually charges, not a headline rate, a discounted introductory rate that will reset, or a rate from another country or another loan type. New Zealand home loans come in fixed, floating, offset and revolving shapes, and the shape changes what the rate means: a fixed rate locks the repayment for the fixed period, a floating rate moves, and an offset or revolving facility changes the balance the interest is charged on. This calculator models a standard amortizing loan at a single rate, and a loan whose rate or balance behaves differently will produce a different repayment, however carefully the inputs are entered.

Finally, the bank’s repayment will differ from this calculator’s for ordinary reasons, and the difference is usually informative rather than alarming. The bank may calculate on a slightly different day count, may include fees, insurance, or a different treatment of the first period, or may be quoting a different loan shape altogether. Compare the principal and interest lines, check the rate and the period conversion, and ask the bank to explain any remaining gap, rather than assuming either figure is wrong. The calculator’s job is to give a verified figure to compare against, not to replace the bank’s offer.

Refinancing from the five-year balance

After five years on the default loan, the balance is NZ$561,665.86. That balance, not the original NZ$600,000, is what any refinance or restructure starts from.

Five years of payments at NZ$3,792.41 total about NZ$227,544.60, of which the year-by-year table shows NZ$189,210.35 of interest across years one to five and NZ$38,334.14 of principal, leaving NZ$561,665.86 still owing. A borrower who refinances at that point is borrowing NZ$561,665.86, not NZ$600,000, and the new repayment depends on the new rate, the new term, and whether the remaining term is kept at 25 years or reset. Resetting the term to 30 years lowers the repayment but restarts the interest-heavy early years on a balance that is still over NZ$560,000, and it adds years of interest that the original schedule would not have charged. Keeping the remaining 25 years preserves the original finish date and the original interest shape, at whatever the new rate gives.

The refinance calculation itself is just this calculator with new inputs: the balance as the loan, through a price and deposit that produce it, at the new rate, over the remaining term, with any extra repayment the borrower plans. Run that calculation before accepting a refinance offer, and compare its total interest against the total interest remaining on the current loan, not just its monthly repayment against the current repayment. A refinance that lowers the monthly payment by extending the term can easily raise total interest, and a refinance that raises the monthly payment by shortening the term can lower it. The monthly figure is the least informative number in the offer. The total interest, and the finish date, are the ones to judge it by.

Splitting the loan: certainty and flexibility together

Part fixed and part floating hedges both ways: the fixed portion locks part of the payment, and the floating portion allows free extra repayments. At refixing, lump sums go into the floating portion or into offset, where they cut the interest-bearing balance without locking the money away.

The serviceability test decides approval

Banks test affordability at a rate above the actual rate, to allow for rises. A loan that fits at 6.5 percent may not pass at 8 or 9 percent, and that test, not the repayment figure, decides approval. Enter the offered rate, including any low-equity margin, for a realistic figure.

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