Take a $15,000 debt charging 19.95 percent a year, with a $500 monthly payment. In the first month the interest alone is about $249, so only the other $251 of your payment actually reduces the balance. As the balance falls each month, the interest shrinks and more of every payment goes to principal. Working through month by month, the debt clears in about 3 years and 6 months, and you pay roughly $5,944 in interest along the way.
Now lift the payment to $650 a month. The debt clears in about 2 years and 6 months instead, a full year sooner, and total interest drops to around $4,079. That extra $150 a month saves you close to $1,865 in interest. This is the whole point of paying more than the minimum: at near 20 percent, every extra dollar above the interest charge attacks the balance hard. New Zealand credit cards sit around this rate, which is why clearing them usually beats almost any saving you could earn elsewhere.
Scenario
Time to clear
Total interest
Pay $500 a month
3 years 6 months
$5,944
Pay $650 a month
2 years 6 months
$4,079
Saving from the extra $150
12 months
$1,865
How it is calculated
The calculator simulates the debt one month at a time rather than using a closed formula. Each month it charges interest equal to the current balance times the monthly rate, which is the annual rate divided by 12, adds that interest to the balance, then subtracts your fixed payment. It counts the months until the balance reaches zero and sums the interest charged along the way. There is one important guard: if your payment is less than or equal to the first month’s interest, the balance never falls and the tool warns that the debt will not clear at that payment. Paying above the interest charge is what creates progress, and paying well above it is what saves both time and interest. The avalanche approach, tackling the highest-rate debt first, minimises total interest, while the snowball approach clears the smallest balance first for momentum.
Frequently asked questions
Snowball or avalanche?
The avalanche method pays the highest-interest debt first to minimise interest; the snowball method clears the smallest balance first for quick wins and motivation. Either way, paying more than the minimum is what shortens the payoff. New Zealand credit cards often charge around 20% interest, so clearing them first usually beats any saving.
Are there rules on how lenders must disclose interest in New Zealand?
Yes. The Credit Contracts and Consumer Finance Act 2003 (CCCFA) requires lenders to disclose the annual interest rate, the total amount of credit, all fees, and the total repayment amount before you sign. From 2021 reforms, lenders must also run affordability checks and must not enter contracts they reasonably believe the borrower cannot repay. IRD does not administer consumer credit law; that sits with the Commerce Commission and Financial Markets Authority.
Does KiwiSaver affect debt repayment decisions?
KiwiSaver contributions are compulsory while employed (minimum 3% of gross pay), so they run alongside any debt repayment. From 1 April 2025 the minimum employer contribution also remains 3%. Pausing KiwiSaver through a savings suspension (allowed once you have been a member for one year) frees up cash for debt, but you lose employer contributions and government member tax credits (currently up to $521.43 per year) for that period. For high-rate consumer debt above 15%, the interest saved usually outweighs the lost credits, but each situation differs.
How do hardship provisions work for New Zealand borrowers?
Under the CCCFA, you can apply to your lender for a hardship variation if you are suffering or likely to suffer financial hardship due to illness, injury, loss of employment, end of a relationship, or other reasonable cause. The lender must consider the application and respond. Common outcomes include temporarily reducing payments, extending the loan term, or waiving fees. If the lender declines and you disagree, you can escalate to an approved dispute resolution scheme such as Financial Services Complaints Ltd (FSCL) or Bankers Ombudsman at no cost to you.