Simple Interest Calculator South Africa
Calculate simple interest using I = P × R × T. Instantly find interest earned on savings or the total cost of a loan in South African Rand.
Quick Calculator Get a fast estimate
R
%
yrs
Interest Earned (I = P × R × T)
R 15 000
Total Amount (A = P + I)
R 65 000
Principal
R 50 000
Effective Annual Return
10.00%
Monthly Interest
R 417
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How to Use the Simple Interest Calculator
Enter your principal amount (the starting sum in Rand), the annual interest rate, and the time period in years. Results update instantly — you'll see the interest earned (I), total amount (A = P + I), and monthly interest.
The Extended Calculator below lets you compare savings vs loan scenarios with period-by-period tables and a visual chart showing how simple interest compares to compound interest. The Professional Calculator adds reverse calculations (find rate or time), day-count conventions, and SA bank rate benchmarks.
Need more detail?
Extended Calculator More options, charts, and scenario comparison
R
%
yrs
Total Interest Earned (Simple)
R 17 500
Total Amount
R 67 500
Compound Alternative
R 70 128
Compound Advantage
R 2 628
Simple vs Compound Interest Growth
Monthly Breakdown (first 24 periods)
| Period | Opening | Interest | Closing |
|---|---|---|---|
| Month 1 | R 50 000 | R 292 | R 50 292 |
| Month 2 | R 50 292 | R 292 | R 50 583 |
| Month 3 | R 50 583 | R 292 | R 50 875 |
| Month 4 | R 50 875 | R 292 | R 51 167 |
| Month 5 | R 51 167 | R 292 | R 51 458 |
| Month 6 | R 51 458 | R 292 | R 51 750 |
| Month 7 | R 51 750 | R 292 | R 52 042 |
| Month 8 | R 52 042 | R 292 | R 52 333 |
| Month 9 | R 52 333 | R 292 | R 52 625 |
| Month 10 | R 52 625 | R 292 | R 52 917 |
| Month 11 | R 52 917 | R 292 | R 53 208 |
| Month 12 | R 53 208 | R 292 | R 53 500 |
| Month 13 | R 53 500 | R 292 | R 53 792 |
| Month 14 | R 53 792 | R 292 | R 54 083 |
| Month 15 | R 54 083 | R 292 | R 54 375 |
| Month 16 | R 54 375 | R 292 | R 54 667 |
| Month 17 | R 54 667 | R 292 | R 54 958 |
| Month 18 | R 54 958 | R 292 | R 55 250 |
| Month 19 | R 55 250 | R 292 | R 55 542 |
| Month 20 | R 55 542 | R 292 | R 55 833 |
| Month 21 | R 55 833 | R 292 | R 56 125 |
| Month 22 | R 56 125 | R 292 | R 56 417 |
| Month 23 | R 56 417 | R 292 | R 56 708 |
| Month 24 | R 56 708 | R 292 | R 57 000 |
Simple Interest Formula
I = P × R × T
Where:
I = Interest earned or paid
P = Principal (starting amount)
R = Annual interest rate (as a decimal, e.g. 10% = 0.10)
T = Time in years
Total Amount: A = P + I = P(1 + R × T)
Partial year: T = Days ÷ Day-count basis (365 or 360)
Worked Example — Savings
You deposit R80,000 in a 32-day notice account at 7.5% p.a. for 6 months (182 days)
I = R80,000 × 0.075 × (182 ÷ 365) = R80,000 × 0.075 × 0.4986 = R2,992
Total amount after 6 months: R80,000 + R2,992 = R82,992
Monthly interest: R2,992 ÷ 6 = R499/month
Worked Example — Personal Loan
Personal loan of R30,000 at 22% p.a. over 2 years
I = R30,000 × 0.22 × 2 = R13,200
Total repayment: R30,000 + R13,200 = R43,200
Monthly payment: R43,200 ÷ 24 = R1,800/month
Interest cost as % of loan: 44% — always compare with compound (amortising) loan costs.
SA Interest Rate Context 2026
| Rate/Product | Rate | Notes |
|---|---|---|
| SARB Repo Rate | 7.75% | Base rate set by Reserve Bank |
| Prime Lending Rate | 11.25% | Prime = Repo + 3.5% |
| Savings / Notice | 6–8% | Call and notice accounts |
| Fixed Deposit (12m) | 9–10% | Major SA banks |
| Personal Loan | 15–28% | Unsecured lending |
| Credit Card | ~22.5% | Revolving credit |
Need full precision?
Professional Calculator Complete parameters, sensitivity analysis, and detailed breakdown
Reverse Calculator — Solve For
days
e.g. 365 = 1 year, 90 = 3 months
R
%
Interest
R 11 250
Total: R 111 250 | Effective daily: R 31/day
SA Rate Benchmark Comparison
R
days
| Rate / Product | Rate | Interest Earned | Total |
|---|---|---|---|
SARB Prime Rate Current prime lending rate | 11.25% | R 11 250 | R 111 250 |
Repo Rate SARB repo rate (Mar 2026) | 7.75% | R 7 750 | R 107 750 |
Savings (FNB, Nedbank, Absa) Typical notice account | 6.5% | R 6 500 | R 106 500 |
32-Day Notice Typical 32-day notice deposit | 7.5% | R 7 500 | R 107 500 |
Money Market Unit trust money market fund | 8.2% | R 8 200 | R 108 200 |
Fixed Deposit (12m) Major banks 12-month FD | 9.5% | R 9 500 | R 109 500 |
Personal Loan Typical personal loan rate | 22% | R 22 000 | R 122 000 |
Credit Card Standard credit card rate | 22.5% | R 22 500 | R 122 500 |
Micro-lender (max NCA) NCA max personal loan cap | 29.25% | R 29 250 | R 129 250 |
Rates above prime rate are highlighted in red (loan costs). Savings rates in green. Day-count: Actual/365 (SA bond market).
Frequently Asked Questions
Simple interest is calculated as I = P × R × T, where P is the principal, R is the annual interest rate as a decimal, and T is time in years. For example, R50,000 at 10% for 3 years: I = R50,000 × 0.10 × 3 = R15,000. Total = R65,000.
Simple interest earns interest only on the original principal each period. Compound interest earns interest on both principal and accumulated interest — so interest grows exponentially. Over long periods the difference is significant: R100,000 at 10% for 20 years gives R300,000 (simple) vs R672,750 (monthly compound).
In 2026: SARB prime rate is 11.25% (repo 7.75%). Savings accounts offer 6–8% p.a. Fixed deposits offer 9–10% for 12 months. Personal loans range from 15–28%. Credit cards charge around 22.5%. The NCA caps personal loan rates at prime + 21% = ~32%.
Simple interest is used for short-term SA money market instruments, treasury bills, bridging finance, and some short-term personal loans. The SA bond market uses Actual/365 day-count convention. For mortgages and most personal loans, lenders use amortising schedules (compound interest).
Express time as Days ÷ Basis. For 90 days on Actual/365 basis: T = 90/365 = 0.2466. Interest on R100,000 at 10% = R100,000 × 0.10 × 0.2466 = R2,466. Money market instruments often use Actual/360, giving slightly higher effective rates.