How Credit Scores Work: What Actually Affects Your Number

Your credit score is a three-digit number, usually between 300 and 850, that estimates how likely you are to repay a loan on time. Lenders use it to decide whether to give you credit and what interest rate you’ll pay — and the difference between a fair score and a very good one can mean tens of thousands of dollars over the life of a mortgage. Here’s what actually goes into the number, and just as importantly, what doesn’t.

Quick Answer

The FICO score — used by about 90% of top lenders — is built from five factors in your credit report: payment history (35%), amounts owed (30%), length of credit history (15%), new credit (10%), and credit mix (10%). Things like your income, age, and bank balances are not in your score at all. The two levers that matter most are simple: pay every bill on time, and keep card balances well below your credit limits.

Where the Number Comes From

Your score isn’t a mysterious grade handed down by a bureau. It’s calculated from the information in your credit report — the record of your credit accounts maintained by the three major bureaus: Equifax, Experian, and TransUnion. Lenders report your account activity to the bureaus (usually monthly), and scoring models analyze that data to produce a number. The two main scoring models are FICO and VantageScore; they use similar data but weight it differently, which is why your scores can differ slightly depending on who calculated them and which bureau’s report was used.

The Five Factors (and Their Weights)

FICO publishes the breakdown of its base scores, and the proportions are consistent across the two major models’ priorities:

1. Payment History — 35%

The single biggest factor. Your track record of paying loans and credit cards on time is the strongest predictor of whether you’ll pay future debts as agreed. Late payments (typically reported once they’re 30+ days past due), collections, and bankruptcies all hurt — and the more severe, recent, and frequent the negative mark, the bigger the impact. Most negative information stays on your report for up to seven years; Chapter 7 bankruptcy lasts ten.

2. Amounts Owed — 30%

Not just how much debt you have, but how much of your available credit you’re using — your credit utilization ratio. Add up your card balances, divide by your total limits, and that’s your utilization. Experts generally advise staying under 30%, and people with the best scores tend to use under 10%. One commonly missed detail: scoring models use the balance your issuer reports to the bureaus — usually your statement balance — not what you owe after paying the bill. Even if you pay in full every month, you can have high reported utilization. Making a payment before your statement closes keeps the reported number low.

3. Length of Credit History — 15%

How long your accounts have been open, including the age of your oldest account and the average age of all your accounts. There’s no shortcut here — history takes time. It’s one reason to think twice before closing an old card you no longer use: a closed account in good standing can stay on your report for up to 10 years and keep helping you, though closing it does reduce your total available credit, which can raise your utilization.

4. New Credit — 10%

Applying for credit creates a “hard inquiry” on your report, which can shave a few points off your score. Opening several new accounts in a short window signals greater risk. One protection: rate shopping for a mortgage, auto loan, or student loan is treated specially — multiple inquiries within a 14–45 day window (depending on the model version) count as one. Credit card applications get no such treatment; each one counts separately. Checking your own score is a “soft inquiry” and never hurts you.

5. Credit Mix — 10%

Scoring models look at the variety of your accounts — revolving (cards) versus installment (mortgage, auto, student loans). You don’t need one of each, and this factor matters mostly for people with thin credit files. It’s never worth taking out a loan you don’t need just to diversify your mix.

What’s NOT in Your Score

FICO is explicit that its scores do not consider your income, age, education, employment history, gender, zip code, marital status, or race. Your bank balances and savings aren’t in your credit report, so they aren’t in your score either. A lender may ask about income separately when you apply — but the score itself is built only from your credit report data.

What the Ranges Mean

Base FICO scores run from 300 to 850 and are commonly grouped as: Exceptional (800+), Very Good (740–799), Good (670–739), Fair (580–669), and Poor (below 580). Most lenders treat 670 and above as good. These are general guideposts — every lender sets its own standards for what it will approve and at what rate.

What Actually Improves Your Score

The CFPB’s guidance is refreshingly free of tricks, and it maps directly onto the factor weights:

• Pay on time, every time. Set up autopay or reminders. If you’ve missed payments, get current and stay current — the number one factor by a wide margin.
• Keep balances well below your limits. Under 30% at most, ideally under 10%. Paying in full each month is best — and no, you don’t need to carry a balance to build credit.
• Only apply for credit you need. Space out applications; skip the store card just for the one-time discount.
• Let your history grow. Time plus on-time payments does the work; nothing accelerates it.
• Check your reports and dispute errors. You can get free reports from all three bureaus, and errors do bring scores down. Dispute mistakes with both the bureau and the company that reported the information.
• If you’re starting out, consider a secured card or credit-builder loan. These products exist specifically to help people establish a credit record.

There’s no secret formula and no overnight fix. A score reflects years of payment behavior, and rebuilding it takes time — but the levers are few, well-understood, and entirely in your hands.

Sources & Methodology

The five-factor breakdown and percentage weights were taken from FICO’s own educational materials (myFICO’s “What’s in your credit score” and “Understanding FICO Scores” publications), which is the authoritative primary source since FICO builds the model. Score ranges and the list of excluded factors (income, age, employment history, etc.) also come from FICO. Guidance on improving credit was cross-checked against official US government sources: the Consumer Financial Protection Bureau’s consumer guidance on getting and keeping a good credit score and rebuilding credit, and the Federal Trade Commission’s Credit Scores consumer guide. Details on credit utilization reporting timing, rate-shopping windows, and inquiry treatment were verified against Experian’s credit education pages, and VantageScore’s alternative factor weighting against Fidelity’s learning-center explainer. Claims were kept only where multiple sources agreed; where sources differed (e.g., the 14- vs 45-day rate-shopping window), the article presents the range rather than a single figure. No first-hand credit products or services were tested for this article.