Recently, credit cards have become a widely discussed topic in society. Some view them as a “debt trap,” while others see them as a “financial tool to help manage cash flow.”
In reality, credit cards are neither inherently good nor bad; their impact depends on how well one understands their mechanisms.
For those who understand the system, credit cards can be an effective cash flow management tool. However, using them without grasping how interest is calculated may cause debt to increase faster than anticipated.
This article explores three common misconceptions about credit card interest frequently encountered.
One highlight of credit cards is the grace period, typically lasting about 45–51 days.
During this time, you can spend on your credit card without incurring interest, provided you pay the full balance on time.
However, if you choose to pay only the minimum amount, the interest-free privilege ends immediately, and interest starts accruing from the date of each transaction.
This mechanism often leads many to mistakenly believe that “paying the minimum means interest won’t be significant.”
In reality, interest is calculated retroactively on a daily basis starting from the first transaction within that billing cycle.
According to the Bank of Thailand’s guidelines, credit card interest rates currently have a ceiling of 16% per annum.
This figure may seem low compared to some loans, like cash card loans, but many card users don’t realize that credit card interest accrues daily and, once minimum payment begins, interest is calculated in two phases.
Phase 1: Interest is charged on the total spending from the posting date until the day before payment is made.
Phase 2: After paying the minimum amount, interest is charged on the remaining principal until the next billing statement date.
Here is an example to illustrate the interest calculation.
Assume the following scenario:
If you pay the minimum amount of 1,000 baht on 5 April, the bank calculates interest as follows.
Part 1:
Part 2:
Total interest for the next billing cycle is 153 + 63 = approximately 216 baht.
Thus, 16% interest is not insignificant when the calculation method is understood.
In practice, paying only the minimum reduces the principal balance only slightly each billing cycle because most payments go toward interest first.
If you continue spending on a card with outstanding balances and keep paying only the minimum for several months, your debt may decrease very slowly while interest continues to accumulate every cycle.
Once you understand interest mechanics, disciplined credit card use can follow simple principles.
1. Use the card as a payment tool, not as a borrowing source. Spend only what you can cover with cash on hand.
2. Always pay the full balance each cycle to maintain the 0% interest benefit during the grace period.
3. If you start missing full payments, stop using the card temporarily and gradually pay down the outstanding balance to reduce accumulating debt and interest.
Credit cards are very useful financial tools when used properly.
Those who understand interest calculation can use cards to manage cash flow, accumulate benefits, and enhance convenience. But those unaware of daily interest accrual may see their debt grow faster than expected.
Understanding these underlying numbers is a fundamental step to using credit cards beneficially in life.
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