Interest Rate Calculator
Calculate the interest rate on any loan from the payment amount, loan amount, and term. Reverse-engineer any finance offer to see the true annual rate.
Quick Calculator Get a fast estimate
R
R
The fixed monthly repayment you were quoted.
R
Final lump sum payment at end of term (0 for standard loans).
Annual Interest Rate (Nominal)
1017792412691.18%
Effective Annual Rate (EAR)
1.3859117023953044e+109%
Monthly Interest Rate
84816034390.93%
vs SA Prime Rate (11.75%)
+1 017 792 412 679,43% above prime
Total Amount Paid
R 720 000
Total Interest Paid
R 220 000
Loan Amount
R 500 000
Monthly Payment
R 6 000
Term
120 months
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Nominal vs Effective Rate
When interest compounds monthly (as most SA loans do), the effective annual rate is slightly higher than the nominal rate:
| Nominal Rate | Effective Annual Rate |
|---|---|
| 10.00% | 10.47% |
| 11.75% | 12.38% |
| 15.00% | 16.08% |
| 20.00% | 21.94% |
| 25.00% | 27.74% |
The Extended Calculator lets you find the rate, payment, or term. The Professional Calculator adds APR (including NCA fees) and compounding frequency comparison.
Need more detail?
Extended Calculator More options, charts, and scenario comparison
R
R
yrs
Implied Annual Interest Rate
11.503%
Effective Annual Rate
12.130%
Total Interest Paid
R 2 340 000
Total Paid
R 3 840 000
Monthly Payment vs Interest Rate (20-year loan on R 1 500 000)
How to Find Your Loan Interest Rate
If a lender quotes you a monthly payment without clearly stating the rate, you can reverse-calculate it. Enter the loan amount, the quoted monthly payment, and the loan term. The calculator will tell you the exact annual interest rate — and how it compares to the SA prime rate.
Watch out for: Fees added to the loan amount (initiation fees, service fees), credit life insurance folded into the payment, and balloon payments. These all affect the true cost of credit. Under the NCA, initiation fees are capped at R6,000 (incl. VAT) and monthly service fees at R69.
Need full precision?
Professional Calculator Complete parameters, sensitivity analysis, and detailed breakdown
Rate Conversion
%
| Rate Type | Value |
|---|---|
| Nominal Rate (as stated) | 11.7500% |
| Effective Annual Rate (EAR) | 12.4039% |
| Monthly Rate | 0.9792% |
| Quarterly Nominal Equivalent | 11.8654% |
| Daily Nominal Equivalent | 11.6947% |
Loan & APR Analysis
R
R
NCA cap: R6,000
R
NCA cap: R69/month
Annual Percentage Rate (APR) including fees
11.88%
Monthly instalment (no fees)
R 16 256
Monthly instalment (with fees)
R 16 325
Total interest
R 2 401 345
Compounding Comparison Table
| Frequency | Nominal Rate | Effective Annual Rate |
|---|---|---|
| Monthly | 11.75% | 12.4039% |
| Quarterly | 11.75% | 12.2779% |
| Semi-annual | 11.75% | 12.0952% |
| Annual | 11.75% | 11.7500% |
| Daily | 11.75% | 12.4660% |
Annual Amortization Schedule
| Year | Interest | Principal | Balance |
|---|---|---|---|
| Year 1 | R 175 203 | R 19 864 | R 1 480 136 |
| Year 2 | R 172 739 | R 22 328 | R 1 457 807 |
| Year 3 | R 169 969 | R 25 098 | R 1 432 709 |
| Year 4 | R 166 856 | R 28 211 | R 1 404 498 |
| Year 5 | R 163 357 | R 31 710 | R 1 372 787 |
| Year 6 | R 159 423 | R 35 644 | R 1 337 144 |
| Year 7 | R 155 002 | R 40 065 | R 1 297 079 |
| Year 8 | R 150 033 | R 45 035 | R 1 252 044 |
| Year 9 | R 144 447 | R 50 621 | R 1 201 423 |
| Year 10 | R 138 168 | R 56 900 | R 1 144 524 |
| Year 11 | R 131 110 | R 63 957 | R 1 080 566 |
| Year 12 | R 123 177 | R 71 891 | R 1 008 675 |
| Year 13 | R 114 259 | R 80 808 | R 927 868 |
| Year 14 | R 104 236 | R 90 831 | R 837 036 |
| Year 15 | R 92 969 | R 102 098 | R 734 939 |
| Year 16 | R 80 305 | R 114 762 | R 620 177 |
| Year 17 | R 66 070 | R 128 997 | R 491 180 |
| Year 18 | R 50 070 | R 144 998 | R 346 182 |
| Year 19 | R 32 084 | R 162 983 | R 183 199 |
| Year 20 | R 11 868 | R 183 199 | R 0 |
Frequently Asked Questions
To find the interest rate, you need the loan amount, monthly payment, and term. The calculator uses the Newton-Raphson numerical method to solve for the monthly rate, then multiplies by 12 to get the annual nominal rate. This is more accurate than simple approximations.
The nominal rate is the stated annual rate. The effective annual rate (EAR) accounts for compounding frequency. For monthly compounding: EAR = (1 + nominal/12)^12 - 1. For a 12% nominal rate, EAR = 12.68%. The EAR is the true cost of borrowing.
The SARB prime lending rate in South Africa is approximately 11.75% as of 2025/2026 (repo rate 8.25% + 3.5%). Most variable-rate loans are linked to prime. A rate "above prime" means you are paying more than the benchmark — typically indicating higher risk in the lender's view.