Bond Extra-Payment Savings Calculator ☆ Stoor

Why small extra payments do so much

The result above surprises most people, and the reason is structural. In the early years of a bond, most of each instalment is interest — only a small slice reduces the balance.

An extra payment behaves completely differently: it goes straight at the capital. Because all future interest is charged on that balance, reducing it early removes interest from every remaining month of the loan. That is why a modest extra amount, paid consistently, cuts years off a 20-year bond.

For most South African homeowners this is the highest-return use of spare money. The "return" is your bond rate — currently prime at 10.50% plus or minus your margin — guaranteed, and effectively tax free, since you are avoiding interest rather than earning taxable income.

The comparison that decides it

Overpaying the bond competes with saving or investing the same money. Compare honestly:

• Overpaying saves you your bond rate — say 10.5% — guaranteed, with no tax on the benefit;
• Saving in a deposit account earns interest that is taxable above the R23,800 annual exemption, so the after-tax return is lower than the headline rate;
• Investing may earn more over long periods, but with real risk and — outside a TFSA — dividends tax at 20% and CGT above the R50,000 annual exclusion.

On a risk-adjusted, after-tax basis, overpaying a bond is hard to beat. The main exception is a TFSA, where growth is entirely tax free, and any employer retirement match, which is an immediate guaranteed return.

Three checks before you start

1. Clear more expensive debt first. Cards are capped at 21% and unsecured loans at 28% — both far above a bond rate. Use the debt payoff planner;
2. Keep an emergency fund. Money paid into a bond is hard to retrieve. Overpaying with no buffer means the next emergency is funded by credit at 21–28%, losing far more than the overpayment saved. An access bond mitigates this — see below;
3. Confirm how your bank applies it. Ask three things in writing: are extra payments allowed without penalty; do they reduce the term or the instalment; and are they applied to capital immediately?

The "term or instalment" question matters most

Many banks apply extra payments by reducing your future instalment while keeping the term unchanged. That feels helpful and saves far less interest than keeping the instalment and shortening the term — which is what the calculator above models. If your bank defaults to lowering the instalment, ask whether you can elect to shorten the term instead, and get the election in writing.

Access bonds: the best of both, with a discipline warning

An access bond lets you withdraw the extra you have paid in. That solves the liquidity problem — your overpayments double as an emergency fund earning your bond rate.

The catch is behavioural: money that is easy to withdraw frequently gets withdrawn for things that are not emergencies, and the term never actually shortens. Use it deliberately, or use a fixed extra payment if you know that access would tempt you.

Ways to fund the extra

• Round the instalment up to the next convenient figure and leave it there permanently;
• Keep paying the old amount when rates fall. When prime drops, your required instalment falls — continue paying the previous figure and the difference becomes an automatic overpayment;
• Direct annual money at it — a bonus, a tax refund from your retirement contributions;
• Add part of every raise before it joins your spending.

Frequently asked questions

Is it better to overpay or invest?

Compare your bond rate against a realistic after-tax return. Given a bond around prime and taxable interest above R23,800, overpaying usually wins on a risk-adjusted basis — with a TFSA and an employer match as the main exceptions.

Will my bank penalise extra payments?

Most allow them on variable-rate bonds, but fixed-rate agreements and early full settlement can attract notice requirements or penalties. Confirm before you start.

Does a lump sum beat monthly extras?

Earlier is better, because interest is saved on every remaining month. Test both with your own figures.

Should I overpay or fill my TFSA?

Both are strong. The TFSA's tax-free growth compounds over decades but carries market risk; overpaying is guaranteed. Many people do some of each.

What if rates rise?

Your required instalment rises, but the capital you already removed permanently reduces the interest charged from then on — overpaying early is exactly what cushions a future increase.

Prime is currently 10.50% and moves with SARB decisions. NCA caps (21% credit facilities, 28% unsecured) apply at the current 7.00% repo. Bank rules on extra payments vary — confirm yours in writing. General information, not financial advice.