A $1,000 laptop. $0 of interest, or $886.90?
The story so far Your secured card worked: after 6 months of on-time payments you have a credit score, and a bank gives you a regular credit card with a $1,500 limit. You buy a $1,000 laptop for school with it. If you pay the full $1,000 when the bill comes, you pay $0 of interest. If you pay only the minimum each month, it takes 74 months, more than 6 years, and costs $886.90 of interest. Same laptop. This lesson shows how a card works so you always end up on the $0 side.
A credit card lets you borrow up to a limit and pay it back later. Pay the full bill on time and the loan is free.
Used well, a card builds your credit score, protects you from fraud better than debit, and can pay rewards. Used badly, it's one of the most expensive loans there is.
Spend only what you already have in checking, set autopay for the full statement balance, and never take cash out with it.
Card issuers (banks) lend the money and set the APR. Card networks like Visa and Mastercard move the payments. Credit counselors help people get out of card debt.
What you're looking at: one $1,000 purchase on a card and the two ways it can end. Paid in full, it costs nothing extra. Paid at the minimum, the coins are the $886.90 of interest it adds over 74 months at 24% APR.
How a card bills you.
Every month the card company sends a statement. Learn to read four numbers on it and you'll never pay a cent of interest.
The limit and the statement
Your credit limit is the most you can owe. Once a month the billing cycle ends and the card sends a statement. The statement balance is what you owed when the cycle ended. Anything you buy after that shows up in your current balance and goes on next month's statement.
- Credit limit
- $1,500.
- Statement balance
- The laptop: $1,000. Your utilization that month is $1,000$1,500 = 67%, so next time, pay some of it before the statement closes.
The due date and the grace period
The statement gives a due date, at least 21 days later by law. The time in between is the grace period. Pay the whole statement balance by the due date and you pay no interest at all. That's the whole trick of using a card well.
- Statement
- March 1: you owe $1,000, due March 25.
- Grace period
- Pay $1,000 by March 25 and the laptop cost exactly $1,000. No interest.
- Statement balance
- $1,000.00
- Minimum payment due
- $30.00
- Payment due date
- March 25
- Current balance
- $1,180.00
- Credit limit
- $1,500.00
- Purchase APR
- 24.00%
- Cash advance APR · fee
- 29.99% · 5%
Minimum payment warning: if you make only the minimum payment each month, you will pay off this balance in about 74 months and pay an estimated $886.90 of interest.
What you're looking at: a made-up statement laid out like real ones. The current balance is higher than the statement balance because of $180 you spent after March 1. By law, every statement shows the minimum payment warning at the bottom.
APR: what it costs if you don't pay in full
Leave part of the bill unpaid and the card charges interest at its APR. Card interest is figured daily, but one month works out to about the APR divided by 12. In 2025 the average card APR was about 22% (Federal Reserve). That's why carrying a balance is so expensive: compare it to the 4% your savings earns.
- Monthly rate
- 24%12 = 2% a month.
- One month on $1,000
- $1,000 × 0.02 = $20 of interest.
The minimum payment trap
The minimum payment keeps you from being late, but it's built to barely cover the interest. A common formula is 1% of the balance plus that month's interest, at least $25. Most of each payment goes to interest, so the balance shrinks very slowly.
- First minimum
- 1% of $1,000 = $10, plus $20 of interest = $30. Only $10 of it lowers what you owe.
- Minimum every month
- 74 months and $886.90 of interest, nearly the price of a second laptop.
What you're looking at: what paying off the $1,000 laptop costs at 24% APR, with no new purchases. Slide from "minimum only" to paying it all at once. The bar shows the $1,000 laptop in green and the interest added on in orange.
Fees and the cash trap
Pay late and you get a late fee, often around $30 to $40, and the card may raise your rate to a penalty APR. A payment 30 days late also goes on your credit report, as you saw in Lesson 4.1. A cash advance, taking cash out with your card, costs a fee right away, usually a higher APR, and interest from day one with no grace period. Some cards also charge an annual fee; most starter cards don't.
- Cash advance
- $200 from an ATM with a 5% fee: $200 × 0.05 = $10 before any interest, then 29.99% APR starting that day.
Rewards, and the one rule
Many cards pay cash back, like 1.5% of what you spend. That's real money only if you pay in full: one month of interest wipes it out. Cards also protect you better than debit: your fraud liability is capped at $50, and it's the bank's money that's missing, not yours. The rule: only charge what's already in your checking account, and set autopay for the full statement balance.
- Cash back
- 1.5% of $1,000: $1,000 × 0.015 = $15.
- One month of interest
- $20, more than the whole $15 reward.
Two minutes. Just listen.
Tap any line to jump to it.
Statement day.
Here's your card statement from this lesson. Six questions about it. Read the numbers, then tap your answer. One try each.
What you're looking at: the made-up statement from this lesson, shortened to one line, with a question about it below. Monthly interest uses the monthly rate: 24%12 = 2%.
The logic, step by step.
Four calculations tell you what a card really costs.
Step 1: The monthly rate
- 24% APR
- 24%12 = 2%.
Step 2: One month of interest
- Pay only $30
- ($1,000 − $30) × 0.02 = $970 × 0.02 = $19.40.
Step 3: The minimum payment
- $1,000 balance
- $10 + $20 = $30, so only $10 pays down the laptop.
Step 4: Fees as a percent
- $200 cash advance at 5%
- $200 × 0.05 = $10.
Worked example: three ways to pay for the laptop
- The setup. $1,000 on the card at 24% APR, nothing else added.
- Pay in full by March 25. Grace period: $0 of interest. Total $1,000, and you keep the $15 cash back.
- Pay $100 a month. 12 months, $127.04 of interest. Total $1,127.04.
- Pay the minimum. 74 months, $886.90 of interest. Total $1,886.90.
- The lesson. If you can't pay it in full next month, you can't afford it on a card yet. Save first, using your budget from Unit 3.
A vine you trim every week.
A fast vine like kudzu can grow about a foot a day in summer. Trim it every week and it stays a neat little plant. Skip a few months and it climbs the fence, covers the shed, and takes days of work to cut back.
What you're looking at: an illustration, not data. The same fence and the same kind of vine. On the left it's cut back every week; on the right it was left to grow.
Why this sticks. A card balance grows like the vine, because interest is added on top of interest every month. Paying in full every month is the weekly trim: the vine never gets the chance to spread.
The page you'd copy down.
- Credit limit = most you can owe. Statement balance = what you owed when the cycle ended. Current balance adds newer purchases.
- Grace period: at least 21 days to the due date. Pay the full statement balance by then = $0 interest.
- APR: monthly interest ≈ balance × APR12. 24% → 2% a month. Average card APR about 22% (2025).
- Minimum payment ≈ 1% of balance + interest. $1,000 at 24% → $30 first month, 74 months, $886.90 interest.
- Late: fee (often $30 to $40), maybe a penalty APR; 30+ days late goes on your credit report.
- Cash advance: fee (~5%), higher APR, interest from day one. Avoid.
- Rewards only count if you pay in full. Credit fraud liability: $50 max.
- Rule: charge only what's in checking; autopay the full statement balance.
Fill in the blanks
Grab a friend or a study group.
Read a real statement
With a parent's permission, look at a real card statement together (cover the card number). Find the statement balance, minimum, due date and APR, and the minimum payment warning.
Cost of the minimum
Each person picks something they want, like a phone or a trip. Use the slider in this lesson to find what it costs at the minimum vs. paying $100 a month.
Card or cash?
Take turns naming a purchase. The group decides: put it on a card and pay it off, use debit, or wait and save first. Explain why.
Just you and your money.
These stay on this device. Nobody else sees them.
Exam-style questions.
Written the way a college exam would ask them. Each right answer on the first try is worth 10 xp.
On the job: you're the credit counselor
A client, Devon, asks for help with a credit card. Here are Devon's numbers:
- Card balance: $3,000.
- APR: 24%.
- Devon pays only the minimum, which this month is $90.
- Devon has stopped using the card, so nothing new is being added.
- Devon's budget has room to pay $200 a month.
Your task: tell Devon how much of this month's $90 is interest, how long the minimum would take, and what changes at $200 a month.
See a model answer
This month's interest: 24%12 = 2% a month, and $3,000 × 0.02 = $60. So $60 of the $90 is interest; only $30 lowers the balance.
Minimum only: about 183 months, more than 15 years, and about $4,886.94 of interest.
At $200 a month: paid off in 19 months, with about $602.34 of interest. That saves around $4,284.60 and 13 years.
Next steps: set autopay for $200, keep the card unused until it's paid off, and build a small emergency fund so a surprise doesn't go back on the card.
From your score to your first loan.
What you're looking at: a map of where this lesson fits in the course. Read it left to right: the lesson that comes before, this lesson in the middle, and the lessons it connects to.
- Before · Unit 4Your credit score
- You are hereUse a credit card without getting burned
- Next · Unit 4Loans
- Back · Unit 1Bank fees and fraud
- Back · Unit 3Build an emergency fund