`How Interest Really Works`

If you've ever paid a credit card's minimum for months and watched the balance barely move, this is why: interest is calculated on what you still owe, every single day, and it's added back into that balance before your next payment even lands.

APR vs. daily periodic rate

Your card's Annual Percentage Rate (APR) is a yearly figure, but most issuers charge interest daily using a daily periodic rate — your APR divided by 365. Each day, the issuer takes your balance, multiplies it by that daily rate, and adds the result to what you owe. Do that for 30 days and you get compounding: you're paying interest on interest that was charged earlier in the same billing cycle.

Why the minimum payment trap is so effective

Minimum payments are usually set at around 1–3% of your balance (or a small flat amount, whichever is higher) specifically so that most of each payment covers interest, not principal. On a $5,000 balance at 22% APR, paying only the minimum can take well over a decade to clear and cost more in interest than the original balance itself.

A simple way to see the real cost

Before you commit to a payoff plan, it helps to see two numbers side by side for each debt:

What it tells you	Where to find it
Total interest if you only pay the minimum	Usually printed on your monthly statement — issuers are required to show this
Total interest if you pay a fixed higher amount	Any online loan/credit card payoff calculator

Seeing the gap between those two numbers — often thousands of dollars — is usually what makes people stop paying just the minimum.

Three things that make interest worse than it looks

• Cash advances often start accruing interest immediately, with no grace period, and at a higher APR than purchases.
• Late payments can trigger a penalty APR — sometimes 29%+ — that can apply to your entire balance, not just new charges.
• New purchases on a card you're carrying a balance on typically start accruing interest right away too, since the grace period only applies when you pay the full statement balance.

The takeaway

Every dollar above the minimum you pay goes almost entirely toward principal, which is why extra payments — even $25–$50/month — shrink both your balance and your future interest charges faster than the math seems to suggest. That's the lever the next module's payoff strategies are built around.