How daily mortgage interest works in New Zealand

Daily interest follows the balance through time

A simplified schedule applies the annual rate across each calendar day until the next repayment. The repayment covers accrued interest under the lender’s process and reduces principal with the remainder. Future daily interest is then calculated from a lower balance.

Interest may appear as a monthly charge even when calculated daily. Lenders can use specific cut-off times, day counts and rounding. A calculator should disclose its convention instead of claiming exact agreement with every bank.

Example: direct repayment versus accessible cash

A homeowner has $8,000 that may be needed for repairs. Paying it directly to a standard loan reduces principal but can restrict access. Holding it in a qualifying offset account can reduce the interest-bearing amount while keeping the savings separate, subject to fees and terms.

A revolving-credit balance can also fall when income enters, then rise as bills leave. A one-time calculator input cannot represent that changing daily cash flow. The homeowner models conservative average balances and keeps the products separate.

Prepare a daily-interest scenario

1. Use current principal and contract rate.
2. Enter the next actual repayment date.
3. Choose monthly, fortnightly or weekly frequency.
4. Separate principal extras from offset savings.
5. Do not model revolving-credit redraw as permanent repayment.
6. Compare projected balances with later statements.

Checks that matter more than a formula

Fixed loans can restrict extra repayments or create a break fee, while floating rates can change. Offset and revolving-credit products can have different fees and discipline requirements. Contract terms can outweigh a small timing advantage.

• Ask when payments become effective for interest.
• Check whether leap years use 366 days.
• Confirm which split receives each payment.
• Review rate changes and fixed-expiry dates.
• Use a lender payout quote for final repayment.

Use a calculator as a scenario, not a promise

The New Zealand calculator accrues interest across actual calendar days and discloses a 365- or 366-day basis. Treat it as a consistent comparison method, not the lender’s binding statement.

The New Zealand model accrues interest across actual calendar days, using 365 days or 366 in a leap year. It supports monthly, fortnightly and weekly schedules and treats a stable offset balance separately from principal.

The estimate holds the entered rate constant, assumes extras reach principal and excludes revolving-credit cash flow. Fixed-loan limits, refix rates, break fees, posting and lender rounding can change the actual result.

Review the plan before money leaves

Compare a zero-extra case, the intended plan and an interrupted plan with identical starting inputs. For floating or split debt, rerun at other rates without presenting them as predictions. Stop the projection at a refix date when the next rate is not known.

Keep the loan agreement, latest statement and written lender answers about fixed-loan limits, break fees and payment allocation. Model each split separately when its rate, fixed expiry, offset treatment or flexibility differs.

• Secure required repayments and essential costs first.
• Keep emergency and planned-expense cash accessible.
• Name the intended loan split for an extra payment.
• Verify the transaction and principal on the next statement.
• Rerun after a refix, rate change, fee or product restructure.