Bond repayment calculator with extra payments
Find your monthly instalment, the total interest over the life of the loan, and the effect of paying extra each month or a once-off lump sum.
Your details
Monthly bond instalment
R13 478.13
Paying R14 478.13 a month saves R422 521 in interest
- Total interest
- R1 462 229.75
- Interest saved
- R422 521.09
- Paid off in
- 16 yr 3 mo
How we worked it out
- Loan amountR1 350 000.00
- Monthly instalmentR13 478.13
- Extra monthly paymentR1 000.00
- Once-off extra paymentR0.00
- Months to pay off16 yr 3 mo
- Total interestR1 462 229.75
- Interest saved by extra paymentsR422 521.09
- Time saved3 yr 9 mo
- Assumes a fixed rate for the whole term. Most South African bonds have variable rates linked to prime, so actual costs will change when rates move.
Year-by-year balance
| Year | Interest | Capital repaid | Balance |
|---|---|---|---|
| 1 | R140 165 | R33 573 | R1 316 427 |
| 2 | R136 465 | R37 273 | R1 279 155 |
| 3 | R132 357 | R41 380 | R1 237 775 |
| 4 | R127 797 | R45 940 | R1 191 834 |
| 5 | R122 734 | R51 003 | R1 140 831 |
| 6 | R117 114 | R56 624 | R1 084 207 |
| 7 | R110 874 | R62 864 | R1 021 343 |
| 8 | R103 946 | R69 792 | R951 551 |
| 9 | R96 254 | R77 483 | R874 068 |
| 10 | R87 715 | R86 022 | R788 046 |
| 11 | R78 236 | R95 502 | R692 544 |
| 12 | R67 711 | R106 027 | R586 517 |
| 13 | R56 026 | R117 711 | R468 806 |
| 14 | R43 054 | R130 683 | R338 123 |
| 15 | R28 652 | R145 085 | R193 038 |
| 16 | R12 664 | R161 074 | R31 964 |
| 17 | R465 | R31 964 | R0 |
The formula
Instalment = P × r ÷ (1 − (1 + r)−n), where P is the loan amount, r is the annual rate divided by 12, and n is the number of months. Extra payments are simulated month by month: interest is charged on the balance, then the instalment plus the extra payment reduces it.
Before you sign
- Budget for once-off costs too: see the transfer duty and transfer costs calculator.
- Banks also charge initiation fees and monthly service fees, which are not included here.
- Test your budget at a rate 1–2 percentage points higher than today's to see whether you could afford a rate rise.
Frequently asked questions
How is a bond instalment calculated?
Banks use a standard amortisation formula: interest is charged monthly on the outstanding balance, and a fixed instalment is set so the loan is paid off exactly at the end of the term. Early on, most of each payment is interest.
How much do extra payments save?
Every extra rand reduces the capital immediately, so you stop paying interest on it for the rest of the loan. Even small regular extras can take years off a 20-year bond. The calculator shows the interest and time saved.
Can I take back extra payments?
Many South African bonds have an access facility that lets you withdraw extra payments. Using it puts the interest saving at risk. Check the terms with your bank.
Which interest rate should I use?
Use the rate your bank quotes you. Most home loans are variable and linked to the prime lending rate, so your instalment changes when the Reserve Bank moves rates. The default here is an example only.