What is a credit score, and how do I actually improve it?

A credit score is a three-digit number that lenders use to predict whether you will pay them back. In the US it usually runs from 300 to 850. Higher is better. Under about 670 is considered subprime; over 740 unlocks the best rates.

That is the whole concept. The mystery is in what moves it.

What actually moves the number

Five factors, in rough order of weight:

1. Payment history (~35%) — do you pay your bills on time. A single 30-day late payment can drop your score 50 to 100 points. Nothing matters more.
2. Credit utilization (~30%) — how much of your available credit you are using. If you have a $10,000 limit and a $4,000 balance, your utilization is 40%. Keep it under 30%, ideally under 10%.
3. Length of credit history (~15%) — how long your accounts have been open. This is why closing old credit cards can hurt you.
4. Credit mix (~10%) — a mix of credit cards and installment loans (auto, mortgage, student) helps slightly.
5. New credit (~10%) — opening many new accounts in a short window dings you temporarily.

What does not move it

• Your income. Your salary is not in the formula.
• Your savings or net worth.
• Checking your own score (this is a "soft pull" — harmless).
• Carrying a balance month to month. You do not need to pay interest to build credit. Pay in full and on time.

The fastest legitimate improvements

• Pay every bill on time, automatically. Set up autopay for at least the minimum on everything.
• Pay your card down before the statement closes, not just before the due date. The balance reported to credit bureaus is usually the statement balance.
• Do not close your oldest credit card unless it has a fee you cannot avoid.
• Ask for credit limit increases on cards you already have. A higher limit lowers your utilization without any new debt.

If you do these four things, your score will move. It takes months, not days, but it moves.