
Credit card providers generate revenue through two primary methods. Firstly, they impose transaction fees on businesses such as retailers, restaurants, and other merchants whenever a customer makes a purchase using a credit card. Secondly, they earn money by charging cardholders interest on outstanding balances as well as various fees associated with the use and maintenance of the card.
Key Takeaways
- How Credit Card Interest Works: Credit card interest is charged when you carry a balance past the due date, calculated based on the Annual Percentage Rate (APR). Most credit cards use variable APRs, which fluctuate with market conditions. If unpaid, interest compounds, increasing the total amount owed over time.
- Factors Affecting Credit Card Interest Rates: Interest rates can change due to missed payments, the end of a promotional period, or a decline in credit score. A penalty APR may be applied for late payments, and once an introductory low rate expires, the standard rate takes effect, increasing costs.
- Ways to Avoid Credit Card Interest: Paying your full balance within the grace period prevents interest charges. If full payment isn’t possible, making at least the minimum payment helps reduce late fees and penalty APRs, though interest will still accrue on the remaining balance.
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Understanding Interest Rates in South Africa
An interest rate refers to the cost associated with borrowing money through a home loan, personal loan, credit card, or vehicle financing agreement. It is expressed as a percentage of the total amount borrowed and is applied over the duration of the loan. When repaying a loan, you are required to settle both the original borrowed amount (principal) and the additional percentage-based cost (interest) charged by the lender.
For instance, if you take out a loan of R100 with an annual interest rate of 5%, the interest charged for that year would be R5. As a result, the total repayment amount would be R105 (R100 principal + R5 interest). However, this does not account for additional fees that the lender may apply, which can increase the total cost of borrowing.
Many credit card users don’t fully understand the mechanics of how their spending translates into interest charges. How Does a Credit Card Work? explains the process from transaction to repayment, so you can make informed financial decisions.
What Is Compound Interest?
Compound interest refers to the process where interest is calculated not only on the original amount of money but also on any interest that has been added over time. As interest accumulates, it is reinvested, increasing the total balance, which then earns more interest. This repeated cycle leads to exponential growth of the total amount, a process known as compounding.
This effect can either work in your favour or against you, depending on whether you are saving or borrowing. When saving, compound interest helps your money grow faster, as interest is continuously added to your balance. However, when borrowing, it increases the amount you owe over time, making debt more expensive. Because of this, it is essential to understand interest rates—securing a low rate on debt minimises costs, while a high rate on savings maximises returns.

How Credit Card Interest Works
Credit card interest refers to the cost imposed by credit card issuers for borrowing funds through your card. This charge is generally represented as the annual percentage rate (APR), which determines how much interest you will pay over a year. APRs can be fixed, staying the same over time, or variable, adjusting based on market trends. Some credit cards also offer promotional APRs, which provide temporarily lower interest rates for a set duration before reverting to the standard rate.
Most credit cards apply variable APRs, which are tied to an external benchmark, such as the prime rate. For instance, if the prime rate is 4%, and your credit card applies a 12% margin, your total APR would be 16%. Since the prime rate can change, your APR may increase or decrease accordingly.
When and How Interest Is Charged
In general, interest is only applied if you fail to pay your full balance by the due date. If you carry over a balance from one month to the next, the credit card issuer calculates interest on the outstanding amount and adds it to your balance. This means that in subsequent months, you could end up paying interest on previously accrued interest, which can cause debt to grow quickly if left unpaid.
Credit card issuers provide a grace period, which is the time between the statement closing date and the payment due date. During this period, no interest is charged on new purchases, provided you pay the full balance before the due date. However, if you only make a partial payment, interest is applied to the remaining balance.
To make matters more complex, some credit cards impose different interest rates for various transactions. Purchases may have a lower APR compared to cash advances or balance transfers, which typically carry higher interest rates. Understanding these distinctions is essential to managing credit card debt effectively and avoiding unnecessary interest charges.
Credit cards operate on a revolving credit system, allowing you to borrow, repay, and borrow again. But how does this compare to other revolving credit options? Our guide on What is a Revolving Loan? explains the key differences, helping you better understand your borrowing options.
Types of Credit Card Interest Rates
Credit card interest rates vary based on the type of transaction. While all rates are expressed as Annual Percentage Rates (APR), different rates apply to purchases, cash advances, balance transfers, and penalties. Knowing these distinctions helps in managing costs effectively.
Purchase APR
The purchase APR applies to regular transactions made with your credit card. Interest is only charged if you carry a balance past the due date. Most cards offer a grace period of 20 to 50 days, during which no interest is applied if the full balance is paid. However, if you only make a partial payment, interest accrues on the remaining balance and compounds over time.
Cash Advance APR
A cash advance APR applies when withdrawing cash using your credit card. This rate is typically higher than the purchase APR and does not have a grace period, meaning interest starts accruing immediately. Additionally, cash advances usually come with transaction fees, making them a costly way to access funds.
Balance Transfer APR
The balance transfer APR applies when moving debt from one card to another. Many credit cards offer 0% APR promotional periods, allowing you to pay off debt interest-free for a set time (e.g., 6 to 18 months). However, once the promotion ends, any remaining balance is subject to the standard balance transfer APR, which can be equal to or higher than the purchase APR. A balance transfer fee, typically 2% to 5% of the transferred amount, may also apply.
Penalty APR
A penalty APR is imposed for missed payments or violations of your credit card terms, such as exceeding your limit. This rate can be significantly higher than your regular APR, often reaching 30% or more. Some issuers may reduce the penalty APR after several months of on-time payments, but others may keep it in place indefinitely, increasing borrowing costs.

Factors That May Influence Credit Card Interest Rates
The interest rates on your credit card, also known as Annual Percentage Rates (APRs), are not fixed and can fluctuate due to several factors. If you have observed a sudden rise in your APRs, the following could be some possible explanations:
- Missed Payments: Failing to make your monthly credit card payments on time not only results in late payment fees but may also trigger a penalty APR. This higher interest rate increases the overall cost of your outstanding balance. To revert to a lower APR, consistent and timely payments are required.
- End of Promotional Period: A sharp increase in your APR might indicate that an introductory interest rate offer has expired. Once the promotional period concludes, the bank applies its standard APR to any remaining balances, which can lead to higher interest charges on your outstanding debt.
- Decline in Credit Score: A drop in your credit score may prompt your card issuer to reassess your creditworthiness. If your score decreases significantly, the issuer may consider you a higher risk and, as a result, impose a higher interest rate on your credit card.
Steps for Calculating Credit Card Interest
Understanding how credit card interest is calculated requires looking at the key factors involved. Interest is the cost of borrowing money from your credit provider and is determined by your annual percentage rate (APR) and average daily balance. You can calculate interest charges by following these steps:
Convert the Annual Rate to the Daily Rate
Credit card interest is usually expressed as an Annual Percentage Rate (APR). To determine how much interest is applied daily, divide the APR by 365 days (or 360 days, depending on the lender—check your cardholder agreement for specifics). The resulting daily interest rate is then used to calculate interest charges on your balance for each day of the billing cycle.
Calculate Your Average Daily Balance
The average daily balance is determined by adding up your daily balances throughout the billing cycle and dividing that total by the number of days in the cycle. Your balance fluctuates as you make purchases, payments, or incur additional fees. If your credit card applies compounding interest, the daily balance will also include any previously accrued interest.
To calculate your average daily balance, carefully review your statement, track all transactions for each day, add up the daily balances, and then divide by the total number of days in your billing cycle.
Determine Your Interest Charges
Calculate your daily interest charge by multiplying your average daily balance with the daily interest rate. Then, multiply that result by the total number of days in your billing cycle. The final amount represents the total interest that will be added to your balance for that period.
Considering using a loan to clear your credit card balance? This approach can work in your favour—but only under the right circumstances. Our guide on Should I Pay Off My Debt with a Loan? weighs the pros and cons to help you decide.

Tips to Avoid Credit Card Interest Payments
It is possible to completely avoid incurring interest on your credit card if it is used responsibly. Consider the following methods:
- Settle Your Credit Card Balance in Full: Most banks offer a grace period, typically ranging from 20 to 50 days, between the date of purchase and the due date for payment. If you clear the entire outstanding balance within this timeframe and have not withdrawn cash using a credit advance, no interest will be applied to your account.
- Make at Least the Minimum Payment: If paying the full balance is not feasible, ensure that at least the minimum required payment is made by the due date. This amount is usually around 5% of the total outstanding balance. While this will not prevent interest from accruing on the remaining balance, it will help reduce the overall debt burden and prevent late payment fees and penalty interest charges from being applied.
Conclusion
Understanding credit card interest is essential for managing debt effectively and avoiding excessive charges. Interest is typically applied when a balance is carried beyond the due date, with rates influenced by factors such as creditworthiness, missed payments, and market conditions. By making full and timely payments, taking advantage of grace periods, and being mindful of different APRs for purchases, cash advances, and balance transfers, you can reduce the cost of borrowing. Additionally, maintaining a good credit score and responsible spending habits will help you secure lower interest rates and keep your finances under control.
Frequently Asked Questions
Interest is charged when you do not pay your full balance by the due date. Once the billing cycle ends, any remaining balance is subject to interest, which continues to accrue daily until the amount is fully repaid. If you consistently carry a balance, interest will compound, increasing the total amount you owe over time.
A fixed APR stays the same unless your card issuer notifies you of a change, which typically happens due to policy updates or changes in your credit profile. A variable APR, on the other hand, fluctuates based on market interest rates, such as the prime rate. This means your interest rate can increase or decrease depending on economic conditions, making variable APRs less predictable.
The best way to reduce credit card interest is to pay your full balance on time each month to avoid carrying debt. If full payment isn’t possible, try to pay more than the minimum amount due to reduce the overall interest accrued. Additionally, choosing a credit card with a lower APR, avoiding cash advances, and negotiating a lower rate with your issuer can help reduce interest costs.
No, different types of transactions may have varying interest rates. Standard purchases typically have a lower APR, while cash advances and balance transfers often carry higher interest rates and may not come with a grace period. This means interest on cash advances starts accruing immediately, making them more expensive compared to regular purchases.
Missing a payment can lead to late fees, a penalty APR, and potential damage to your credit score. If a payment is overdue, your issuer may impose a higher interest rate on your outstanding balance, increasing the cost of borrowing. Repeated missed payments may also be reported to credit bureaus, making it harder to qualify for loans or credit in the future. To avoid this, set up payment reminders or automatic payments to ensure timely repayments.
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