Loan Interest Calculator — work out your cost in seconds
Updated:
Total interest
R 78,90
Total repayable
R 1 078,90
Estimate using simple interest: interest = amount × (rate / 100) × (term in days / 365). Actual terms vary with fees and the lender's policy.
Above this text you will find the loan interest calculator from CreditGenius. Enter the loan amount, the annual interest rate, and the term in days, and you will instantly see the total interest you will pay and the total repayment amount. It is the most direct tool for estimating what borrowing costs before you apply.
In this section we explain how the calculation works, what formula it uses internally, what the difference is between simple and compound interest, and why the figure shown here is not exactly the full cost of a loan that also carries fees. If you need to compare two offers with different fee structures, go to the APR calculator. If you want to see an estimated monthly instalment for a loan amortised over several months, the loan calculator is the right tool.
How to use the calculator
The calculator has three inputs. Each maps directly to the simple interest formula, so you will see the effect immediately:
- Amount (R). The capital you will receive. Through CreditGenius the range runs from R500 for a quick loan up to R8 000 for a larger personal loan. The higher the amount, the greater the interest in Rand — even if the percentage rate stays the same.
- Annual interest rate (%). The nominal interest rate expressed as an annual percentage. If the offer says “18% per year”, enter 18. This is the “pure price” of the money, excluding fees.
- Term (days). How many days the loan runs from the date you receive the funds to the repayment date. The formula pro-rates automatically: 91 days is roughly a quarter of a year, 120 days is approximately a third. You do not need to convert to months.
The result is two figures: the total interest you will pay in Rand, and the total repayment amount (principal plus interest). Adjust the inputs freely — the calculation runs locally in your browser, nothing is sent to CreditGenius and nothing is recorded.
The simple interest formula
The calculator applies the standard simple interest formula:
interest = amount × (annual rate / 100) × (term in days / 365)It is straightforward, linear, and used by the majority of short-term consumer loans in South Africa. Here is a concrete example: you borrow R2 000 at 24% per year for 120 days.
- Amount: R2 000
- Annual rate: 24% → 0.24 as a decimal
- Term: 120 days → 120/365 = 0.3288 of a year
Applying the formula: R2 000 × 0.24 × (120/365) = R157.81 in interest. The total to repay is R2 000 + R157.81 = R2 157.81.
That is the pure interest cost of the loan, without fees. Under the NCA, lenders may also charge an initiation fee and a monthly service fee — those are not included here. This calculator focuses on interest only; fees are incorporated in the APR calculator.
Simple interest vs compound interest
There are two ways to calculate interest, and it is worth knowing which one applies to your loan:
- Simple interest. Interest is always calculated on the original principal. If you borrow R1 000 at 10% for one year, you pay R100 in interest, full stop. This is the standard for consumer loans in South Africa: quick loans, short-term loans, and most personal loans. This calculator uses simple interest.
- Compound interest. Interest is added to the principal and, in the next period, interest is calculated on interest. The formula is
principal × (1 + i)^n - principal. The snowball effect is most visible over long horizons: R1 000 at 10% compounded annually over 10 years grows to R2 594, not R2 000.
Compound interest is the norm in complex financial products: long-term savings and investment accounts, bonds, and certain structured loan arrangements. In short-term consumer loans you will rarely encounter it, so for your typical use case this simple interest calculator is the correct one.
Limitations of this calculation
Read this before making decisions based solely on this calculator:
- Does not include fees. The result is pure interest on the annual rate you enter. If the offer carries an NCA initiation fee, monthly service fee, or credit life insurance premium, the actual cost will be higher. For the full effective cost, use the APR calculator.
- Not a binding offer. The interest rate you enter is your own estimate, not necessarily the rate the lender will apply to you. A lender assesses your profile and may offer a different rate depending on the amount, term, income, and credit history.
- Assumes simple interest. If your product uses compound interest (rare in short-term consumer loans), these figures do not apply.
- Does not calculate monthly instalments. It gives you the total interest cost in Rand for a single term, not an amortisation schedule with monthly payments. For that, use the loan calculator.
When to use this calculator
It is the fastest tool for two specific situations:
- Comparing interest between two offers with the same structure. If you have two consumer loan offers with different interest rates but the same term, this calculator tells you how much you pay in interest on each. For comparisons where fees also differ, move to the APR calculator.
- Estimating the cost before applying. Before filling in an online application, calculate the expected interest for your amount and term. If the cost works for you, proceed; if not, adjust before submitting. It takes under a minute and helps you avoid surprises.
From calculating to the next step
Once you are clear on the amount, the term, and the interest cost that suits your budget, the next step is to submit your details through the online application so that lenders can assess your request. Through CreditGenius you receive a real offer in minutes — with the interest rate, APR, and repayment amount confirmed — so you can compare it with your calculations before you commit.
Ready to take the next step? Apply online at CreditGenius — the form takes less than two minutes.
Frequently asked questions
Does the calculator include fees?
No. This calculator applies only the simple interest formula using the annual interest rate you enter, without adding initiation fees, service fees, or credit life insurance premiums. The result is the pure interest you pay on the borrowed amount over the stated term — nothing more. If the loan offer includes compulsory fees, your actual cost will be higher than the figure shown here. To factor in fees and get the true annualised cost of the loan, use the [APR calculator](/apr-calculator/), which incorporates them into the calculation.
What if my loan term is 91 days instead of 365?
The formula pro-rates interest by the fraction of the year the loan runs. If you borrow R1 000 at 12% per year for 91 days, the interest is R1 000 × 0.12 × (91/365) = R29.92 — not R120. The annual rate is expressed over a full year, so you only pay the portion that matches the time you hold the money. The calculator makes that adjustment automatically: enter the actual number of days and you get the interest for that exact term, without rounding to months or full years.
How is compound interest calculated?
Compound interest adds earned interest back to the principal each period, so the next period's interest is calculated on a growing balance. The formula is principal × (1 + i)^n minus the original principal, where i is the periodic rate and n is the number of periods. This calculator does not use compound interest because the vast majority of short-term consumer loans in South Africa work on simple interest. Compound interest appears in more complex financial products such as bonds, long-term savings accounts, or certain restructured loans.
Why might the APR show a different number?
Because APR (Annual Percentage Rate) does not calculate interest alone — it adds the compulsory fees of the loan (NCA initiation fee, monthly service fee) and annualises the total cost. This calculator stops at the pure interest rate, so its figure will always be equal to or lower than the loan's official APR. The APR also assumes a standard annual horizon, while here you see the interest in Rand for your specific term. To understand the difference and compare two offers properly, go to the [APR calculator](/apr-calculator/).
Can I use this calculator for a bond or home loan?
It is not the right tool for that. Home loans use French amortisation with equal monthly instalments over 20 or 30 years, not simple interest over a single term. The correct calculation involves a declining outstanding balance, interest on that decreasing capital, and instalments that blend both elements. For a bond you need a dedicated amortisation schedule simulator. This calculator is designed for short-term consumer loans: quick loans, personal loans, and cash loans where simple interest applies.
What happens if I enter 0% interest?
If you enter 0%, the interest is zero regardless of the amount and term. You repay exactly what you borrowed. This is the typical condition on a first loan through CreditGenius for new borrowers who repay on time: 0% interest and 0% APR means zero cost. One thing to note: if the rate is 0% but the offer includes fees, this calculator will still show R0 because it only looks at interest — the real APR would no longer be 0%. Always check your loan agreement for any fees that apply.
Is this calculator suitable for quick loans?
Yes — that is exactly the use case it is built for. [Quick loans](/quick-loans/) and short-term loans are typically for 91–120 days with an annualised interest rate: enter those three values and you get the interest in Rand instantly. Remember that the figure shown is pure interest, without fees. On short-term loans, fees can be proportionally significant given the brief term, so it is worth cross-checking with the APR afterwards. Even so, this calculator is the fastest way to make a first estimate of the cost.
Can I simulate the effect of settling early?
Indirectly, yes. If the loan is for 120 days and you settle at 91 days, recalculate using 91 days instead of 120: the interest figure you get is what you will actually have paid for the time you held the money. Note that many lenders charge an early settlement fee under the NCA (typically a small percentage of the outstanding balance), which this calculator does not include. Check that fee in your loan agreement before settling early to confirm whether it makes financial sense.
