Compound Interest Calculator
Calculate how your investment grows over time with compound interest. Enter your initial deposit, monthly contributions, interest rate, and investment period to see your total wealth at any future date.
Quick Calculator Get a fast estimate
R
R
%
yrs
Total Investment Value
R 1 885 141
Total Deposited
R 530 000
Interest Earned
R 1 355 141
Growth on Deposits
255.69%
Future Value of Initial Deposit
R 366 404
Future Value of Contributions
R 1 518 738
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How to Use the Compound Interest Calculator
- Initial Deposit: The lump sum you invest today. Enter 0 if starting from scratch.
- Monthly Contribution: The amount you add each month. Consistent contributions dramatically accelerate growth.
- Annual Interest Rate: Your expected return per year. SA balanced funds typically return 10–12%.
- Investment Period: How many years you plan to invest. Time is the most powerful factor.
- Compounding Frequency: How often interest is calculated. Monthly is standard for most SA investments.
The Extended Calculator below adds a growth chart, goal planner, and rate comparison tool. The Professional Calculator provides multi-account portfolio analysis, inflation adjustment, and tax impact by account type.
Need more detail?
Extended Calculator More options, charts, and scenario comparison
R
R
%
Final Balance after 20 Years
R 1 885 141
Total Contributions
R 530 000
Interest Earned
R 1 355 141
Interest %
71.9%
Investment Growth Over Time
Year-by-Year Table
| Year | Balance | Contributions | Interest |
|---|---|---|---|
| 1 | R 80 367 | R 74 000 | R 6 367 |
| 2 | R 113 913 | R 98 000 | R 15 913 |
| 3 | R 150 973 | R 122 000 | R 28 973 |
| 4 | R 191 913 | R 146 000 | R 45 913 |
| 5 | R 237 140 | R 170 000 | R 67 140 |
| 6 | R 287 102 | R 194 000 | R 93 102 |
| 7 | R 342 297 | R 218 000 | R 124 297 |
| 8 | R 403 271 | R 242 000 | R 161 271 |
| 9 | R 470 630 | R 266 000 | R 204 630 |
| 10 | R 545 042 | R 290 000 | R 255 042 |
| 11 | R 627 246 | R 314 000 | R 313 246 |
| 12 | R 718 058 | R 338 000 | R 380 058 |
| 13 | R 818 379 | R 362 000 | R 456 379 |
| 14 | R 929 206 | R 386 000 | R 543 206 |
| 15 | R 1 051 637 | R 410 000 | R 641 637 |
| 16 | R 1 186 888 | R 434 000 | R 752 888 |
| 17 | R 1 336 302 | R 458 000 | R 878 302 |
| 18 | R 1 501 361 | R 482 000 | R 1 019 361 |
| 19 | R 1 683 704 | R 506 000 | R 1 177 704 |
| 20 | R 1 885 141 | R 530 000 | R 1 355 141 |
Compound Interest Formula
Future Value = FV(Lump Sum) + FV(Contributions)
Lump sum: A = P × (1 + r/n)^(n×t)
Regular contributions: FV = PMT × ((1 + r/n)^(n×t) − 1) / (r/n)
- P = Initial deposit
- PMT = Regular contribution per compounding period
- r = Annual interest rate (decimal)
- n = Compounding periods per year
- t = Years
Worked Example
Deposit: R50,000 | Monthly contribution: R2,000 | Rate: 10% | Period: 20 years | Monthly compounding
- Monthly rate: 10% ÷ 12 = 0.8333%
- Total periods: 20 × 12 = 240
- FV of lump sum: R50,000 × (1.008333)^240 ≈ R366,094
- FV of contributions: R2,000 × ((1.008333)^240 − 1) / 0.008333 ≈ R1,519,132
- Total value: R1,885,226
- Total deposited: R50,000 + R2,000 × 240 = R530,000
- Interest earned: R1,885,226 − R530,000 = R1,355,226
Need full precision?
Professional Calculator Complete parameters, sensitivity analysis, and detailed breakdown
Global Settings
%
SA long-run avg ~5.5%
R
Drawn down from all accounts
Investment Accounts
R
R
%
R
R
%
Total Portfolio Value (Nominal)
R 5 179 511
Real Value (After Inflation)
R 1 775 168
After-Tax Value
R 4 912 391
Inflation Used
5.5%
Account-by-Account Results
| Account | Type | Final | Real | After-Tax |
|---|---|---|---|---|
| TFSA | TFSA | R 2 644 510 | R 906 350 | R 2 644 510 |
| Unit Trust | Taxable | R 2 535 000 | R 868 818 | R 2 267 880 |
| Total | R 5 179 511 | R 1 775 168 | R 4 912 391 | |
Year-by-Year Projection — TFSA
| Year | Nominal | Real Value | After-Tax |
|---|---|---|---|
| 5 | R 314 577 | R 240 693 | R 314 577 |
| 10 | R 749 887 | R 439 007 | R 749 887 |
| 15 | R 1 466 107 | R 656 718 | R 1 466 107 |
| 20 | R 2 644 510 | R 906 350 | R 2 644 510 |
Frequently Asked Questions
Compound interest is interest earned on both your principal and previously earned interest. It causes investments to grow exponentially — the longer you invest, the more powerful the effect.
For a lump sum: A = P(1 + r/n)^(nt). For regular contributions, add the annuity formula: PMT × ((1+r/n)^(nt) − 1) / (r/n).
More frequent compounding generates slightly higher returns. Monthly compounding at 10% gives an effective annual rate of about 10.47%, versus exactly 10% when compounding annually.
SA balanced funds have historically returned 10–14% annually before fees. Equity funds can return 12–16%; money market funds return closer to 7–9%. Always consider inflation (4–6% in SA) for real returns.