Extra Repayments Calculator
See the interest and years saved by regular or one-off extra mortgage repayments, computed on a dated schedule rather than a shortcut formula. Working shown.
Repay interest only for the first years, then principal and interest.
Enter your loan and an extra repayment to see the interest and time saved.
Summary
Two ledgers run on identical dates: one with your extra repayments, one without. The difference between their interest totals and their period counts is what is reported as saved.
Working
- §13.5 payment: the scheduled repayment solves P = B·i ÷ (1 − (1 + i)^−n) from the balance B, the periodic rate i and the remaining periods n.
- §13.7 recurrence: each period: interest = accruing balance × i, then closing = opening + interest + fees − payment − extra repayment.
- §13.9 offset: interest accrues on max(0, balance − offset × effectiveness), floored at zero; offset cash is never a principal repayment.
- §12.5.8 reconciliation: the ledger identity is checked on every period. A reconciliation failure invalidates the result rather than warning about it.
Assumptions
- Interest accrues once per repayment period on the payment-period ledger. Daily accrual is not modelled at P0.
- The first repayment falls on 1 October 2026; every date in the schedule follows from that and the repayment frequency.
- The rate is held constant except where a dated rate-change event moves it.
- Weekly, fortnightly and monthly frequencies use 52, 26 and 12 periods per year.
Limitations
- Lender daily accrual, transaction timing, fee timing and rounding can differ from this model; compare the settings with your loan contract and statements.
- Redraw availability, offset eligibility conditions, break costs and any lender fee that was not entered are not modelled.
- Amounts beyond the entered term are not projected; a balance left unpaid at term is reported rather than extended.
Common questions
How much interest do extra mortgage repayments save?
The saving is the difference between two full schedules: your loan with the extra repayments and the same loan without them, each run repayment by repayment on a scheduled ledger. Because every extra dollar reduces the balance that the next period charges interest on, the saving compounds and cannot be read off a simple formula. The result shows interest saved, time saved and the interest total under each schedule side by side.
How do extra repayments shorten a home loan term?
An extra repayment goes entirely to principal, so the balance entering the next period is lower and more of the scheduled repayment goes to principal from then on. The loan closes when the ledger reaches a zero balance, which happens earlier than the contracted term. The calculator reports the new payoff date, the number of repayments under each schedule and the years and months saved.
Is it better to make regular extra repayments or one lump sum?
The calculator prices both and shows the difference rather than ranking them: enter an amount per repayment period, a one-off lump sum on a chosen date, or both. A lump sum paid earlier sits against the balance for more periods, while regular extras build up gradually. The ledger applies each on its own date so timing is reflected, not assumed. Compare the two interest-saved figures to see the trade-off in dollars.
Do extra repayments stay available if I need the money back?
Money paid into the loan reduces the balance and whether you can draw it back depends on the redraw terms in your contract, which this calculator does not model. Money held in an offset account instead reduces the interest charged while remaining yours to withdraw. The comparison panel shows both paths on the same loan so the interest saving and the access difference are visible together.
Does the calculator account for extra repayment limits or fees?
No. Annual extra repayment caps, break costs on fixed rates and redraw fees vary by contract and are not modelled here, which the limitations panel states. The schedule assumes every extra repayment you enter is accepted on its date. Check the caps in your loan contract before treating the saving as achievable.
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