Paying the minimum on a credit card keeps the account in good standing and barely reduces the balance. The figure is calculated to produce exactly that outcome.
The formula favours the lender's revenue
Minimums are typically set as a small percentage of the balance, or a fixed floor amount, whichever is greater.
The percentage is chosen so that it covers the interest charged plus a modest amount of principal, which means the balance falls but very slowly.
Because the payment is calculated on the outstanding balance, it shrinks as the balance shrinks, and the repayment period stretches out accordingly.
The declining payment is the crucial feature
A fixed monthly payment repays a balance in a predictable and finite period, since each payment covers less interest and more principal as the balance falls.
A minimum that declines with the balance removes that acceleration, because the payment falls at roughly the same rate as the interest does.
The result is a repayment period measured in many years for a balance that a modest fixed payment would clear in a fraction of the time.
Interest accrues on the daily balance
Card interest is generally calculated on the balance each day rather than on the statement figure, so the timing of payments affects the amount charged.
New purchases added while a balance is carried begin accruing immediately, which means the balance can grow despite payments being made on time every month.
This is why minimum payments combined with continued use produce a balance that appears stubbornly fixed for long periods.
Disclosure exists because the effect is opaque
Statements in many jurisdictions must show how long repayment would take at the minimum, alongside the payment required to clear the balance within a defined period.
The requirement exists precisely because the arithmetic is counterintuitive, and the comparison between the two figures is usually the most informative line on the statement.
Where such disclosure was introduced, the observable response was a rise in customers paying fixed amounts above the minimum rather than the minimum itself.
Fixing the payment is the practical change
Continuing to pay the original minimum amount as the balance falls, rather than the recalculated one, converts a declining payment into a fixed one.
That single change shortens repayment dramatically without requiring any increase in what is being paid today.
Automating the fixed amount is what makes it stick, since the alternative requires overriding a lower figure that the statement presents as sufficient every month.