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Money Mechanics / Topics / Credit & Borrowing
Credit & Borrowing · Guide

Credit Cards

A credit card is a power tool: fast, useful, and expensive if you don't read the manual. Here's how the machine works, what to check when it acts up, and the rights that come standard.

TypeGuide
LevelStart here
CostFree to read
SectionsStart · Problems · Rights · How-to
Start here

The things that trip people up

Get these straight first — the rest of the guide reads clean once you have them.

Interest accrues daily, not monthly

Most issuers calculate interest every day on your outstanding balance. Carry $1,000 for ten days and you pay ten days of interest on it — which is why paying anything earlier in the cycle costs you less than waiting for the due date.

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Fixed vs. variable APR

A variable APR moves with an interest-rate index; a fixed APR doesn't — but 'fixed' isn't 'forever.' Check which type your card carries before you compare offers, because two cards with the same rate today can cost very differently next year.

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Your terms can change — with notice

Issuers can generally change your terms for future purchases, but significant changes typically require advance written notice (45 days under federal rules). That notice window is your chance to pay down, opt out, or switch cards.

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Key terms8 terms
APR
Annual Percentage Rate — the yearly cost of borrowing on the card, including interest. The number that makes cards comparable.
Grace period
The window between your statement closing and the due date when paying in full means no interest on new purchases. Carry a balance and the grace period usually disappears.
Daily periodic rate
Your APR divided by 365 — the rate actually applied to your balance each day.
Balance transfer
Moving debt from one card to another, usually chasing a lower promotional rate. Watch the transfer fee and what the rate becomes when the promo ends.
Trailing interest
Interest that shows up after you 'paid in full' — charged on the days between your last statement and the day your payment landed.
Credit utilization
Your balance as a share of your limit. Keeping it low helps your credit score.
Unauthorized use
Charges you didn't make or approve. Federal law strictly limits what you can owe for them.
Prescreened offer
A card offer mailed because a bureau matched you to the issuer's criteria. You can opt out of receiving them.
Common problems

When it acts up

What’s actually happening, and the fix.

You paid in full but still got charged interest

That's trailing (residual) interest — interest accrued between the statement date and the day your payment arrived. One more full payment usually clears it. Fix →

Your limit came back lower than expected

Limits are set from income, existing debt, and credit history. You can ask the issuer to reconsider — and a few months of on-time use often earns an increase. Fix →

A charge was declined as 'not authorized'

Usually a fraud-screen trip, a hold on the account, or a limit issue. Call the number on the card — not the merchant — to find out which. Fix →

STD

Your rights

Protections most people don’t know they have — they come standard.

  • The rate on your existing balance generally can't be raised unless your payments fall behind — increases mostly apply to new purchases, with notice. Learn more
  • Report a card lost or stolen before it's used and you owe nothing on unauthorized charges; even reported after, your liability is capped by federal law. Learn more
  • You can dispute billing errors in writing, and the issuer must investigate — you don't have to pay the disputed amount while they do. Learn more
Escalation

Tried the issuer and gotten nowhere? File a complaint with the CFPB at consumerfinance.gov/complaint — companies generally respond within 15 days. Your state attorney general's office is a second route.

How-to

The jobs you’ll actually do

Step-by-step, in plain language.