Your credit score is a three-digit number that determines the interest rate you pay on a mortgage, whether you get approved for an apartment lease, and sometimes whether you get hired for a job. It affects hundreds of thousands of dollars in lifetime borrowing costs. Yet most people have only a vague understanding of how the number is calculated. This guide breaks down the exact factors, their relative weights, and the specific actions that move the needle — backed by data from FICO, Experian, and the Consumer Financial Protection Bureau.
FICO scores, used by approximately 90% of U.S. lenders, are built from five categories of data pulled from your credit reports at Equifax, Experian, and TransUnion. Each category carries a specific weight:
| Factor | Weight | What It Measures |
|---|---|---|
| Payment History | 35% | Whether you pay on time, every time |
| Amounts Owed (Utilization) | 30% | How much of your available credit you are using |
| Length of Credit History | 15% | How long your accounts have been open |
| Credit Mix | 10% | Variety of account types (cards, loans, mortgage) |
| New Credit | 10% | Recent applications and new accounts |
Source: myFICO.com. Weights are approximate and can vary slightly based on individual credit profiles.
Two factors — payment history and utilization — account for 65% of your score. This means the two most impactful things you can do are pay on time and keep balances low. Everything else is secondary.
Payment history is the single largest factor. FICO evaluates whether you have paid all credit accounts on time, including credit cards, installment loans, mortgages, retail accounts, and finance company accounts.
How late payments are scored: The severity depends on how late the payment was, how recently it occurred, and how many late payments you have. A payment reported 30 days late is less damaging than 60 days, which is less damaging than 90+ days. A single 30-day late payment can drop a good score (740+) by 60–110 points, according to FICO's research data. Multiple late payments are worse but not proportionally — the first one does the most damage.
The 30-day threshold matters. If you miss a payment due date by a few days, your credit card company will charge a late fee, but most creditors do not report to the credit bureaus until you are at least 30 days past due. This means a payment that is 5 or 15 days late may cost you a $25–$40 fee but will likely not affect your credit score. Once it crosses 30 days, the damage is significant and immediate.
Practical advice: Set up automatic minimum payments on every credit account. This does not mean you should only pay the minimum — it means you should never miss a payment because you forgot. Pay the full balance when you can, but autopay the minimum as insurance. A single missed payment can undo years of perfect history.
Credit utilization is the ratio of your current credit card balances to your total credit limits. It is calculated both per-card and across all cards combined. FICO looks at both the individual and aggregate numbers.
| Utilization Range | Impact on Score | Example ($10,000 Total Limit) |
|---|---|---|
| 0% | Slightly negative (shows no activity) | $0 balance |
| 1–9% | Optimal | $100–$900 balance |
| 10–29% | Good | $1,000–$2,900 balance |
| 30–49% | Fair (starts hurting) | $3,000–$4,900 balance |
| 50–74% | Poor | $5,000–$7,400 balance |
| 75–100% | Very poor | $7,500–$10,000 balance |
The key insight about utilization: it has no memory. Unlike payment history (where a late payment damages your score for years), utilization is a snapshot of your current balances. If your utilization drops from 60% to 8% in a single billing cycle, your score reflects the new lower number immediately. This makes utilization the fastest lever for improving your credit score. Use the Credit Utilization Calculator to see where you stand and model different paydown scenarios.
An important nuance: 0% utilization across all cards is actually slightly worse than 1–9%. The scoring model wants to see that you use credit responsibly, not that you never use it at all. The ideal is a small balance that you pay in full each month, reported to the bureaus before you pay it off.
FICO considers the age of your oldest account, the age of your newest account, and the average age across all accounts. Longer history is better because it gives lenders more data to evaluate your reliability.
This factor is why financial advisors recommend never closing your oldest credit card, even if you rarely use it. Closing it removes the account from your average age calculation (eventually) and reduces your total available credit (increasing utilization). If the card has no annual fee, keep it open and use it for a small recurring charge to keep it active.
For young adults building credit, this factor works against you purely by mathematics. There is no shortcut — time is the only way to increase credit history length. Being added as an authorized user on a parent's long-standing card can help, as the card's full history may appear on your credit report.
FICO rewards borrowers who demonstrate responsible management of different types of credit. The two broad categories are revolving credit (credit cards, HELOCs) and installment credit (mortgages, auto loans, student loans, personal loans).
Having only credit cards is not as strong as having credit cards plus an installment loan. However, this factor is only 10% of your score, so you should never take out a loan you do not need just to improve your credit mix. The benefit is too small to justify paying interest on an unnecessary loan.
When you apply for credit, the lender performs a hard inquiry on your credit report. Each hard inquiry can lower your score by approximately 5–10 points and remains on your report for two years (though FICO only considers inquiries from the past 12 months in scoring).
Rate shopping exception: FICO recognizes that comparing rates for a mortgage, auto loan, or student loan is smart behavior, not risky borrowing. Multiple hard inquiries for these loan types within a 14–45 day window (depending on the FICO version) are counted as a single inquiry. This means you can shop rates from five mortgage lenders in a two-week period and it counts as one inquiry on your score.
This exception does not apply to credit card applications. Five credit card applications in a month equals five separate hard inquiries.
The financial impact of credit scores is measured in interest rates. Here is what different score ranges typically translate to in real borrowing costs:
| FICO Score | 30-Year Mortgage Rate (approx.) | Monthly Payment ($350K loan) | Total Interest Over 30 Years |
|---|---|---|---|
| 760–850 | 6.50% | $2,212 | $446,320 |
| 700–759 | 6.72% | $2,265 | $465,400 |
| 680–699 | 6.90% | $2,308 | $480,880 |
| 660–679 | 7.11% | $2,359 | $499,240 |
| 620–659 | 7.54% | $2,462 | $526,320 |
Rates are illustrative based on typical lender tiering. Actual rates vary by lender, market conditions, and other factors. The difference between the best and worst tier shown here is approximately $80,000 in total interest over the life of the loan. Use the Mortgage Calculator to model your specific scenario.
The gap between a 760 score and a 620 score costs roughly $250 per month and $80,000 over the life of the loan on a $350,000 mortgage. Similar patterns apply to auto loans, credit cards, and insurance premiums. Credit score optimization is one of the highest-return financial activities you can undertake.
Pay down credit card balances. Dropping utilization from 50% to under 10% can boost your score by 50–100+ points within one billing cycle. This is the single fastest way to improve your score. If you cannot pay down all cards, focus on the card with the highest utilization percentage first.
Dispute errors on your credit report. According to the Federal Trade Commission, approximately one in five consumers has a verified error on at least one of their three credit reports. Common errors include accounts that are not yours, incorrect balances, and late payments that were actually on time. Dispute errors directly with each bureau (Equifax, Experian, TransUnion) through their online portals.
Become current on all accounts. If you have any accounts currently past due, bringing them current stops additional negative reporting. The damage from previous late payments remains, but halting the ongoing delinquency prevents further score decline.
Request a credit limit increase. If you have good payment history, call your card issuers and ask for a higher limit. This instantly reduces your utilization percentage without paying down any balance. Some issuers can process this as a soft inquiry (no score impact), while others perform a hard inquiry — ask before they pull your credit.
Stop applying for new credit. Every application adds a hard inquiry and lowers your average account age. If you are planning a major purchase (home, car), avoid opening new credit accounts for 6–12 months before applying.
Keep old accounts open. Your oldest credit card contributes to the length of your credit history. Even if you never use it, keeping it open (with occasional small charges to prevent closure) helps your score.
Add an installment loan to a credit-card-only profile. If your only credit accounts are credit cards, adding a small personal loan or credit-builder loan adds credit mix diversity. But only do this if you need the loan for another purpose — the 10% weight of credit mix rarely justifies paying interest on an unnecessary loan.
Myth: Carrying a balance improves your score. This is false. Paying your statement balance in full every month gives you the best possible payment history and keeps utilization low. Carrying a balance costs you interest but provides zero scoring benefit.
Myth: Closing unused cards helps your score. Almost always false. Closing a card reduces your total available credit (increasing utilization) and eventually removes the account's history from your average age calculation. Close a card only if it has an annual fee you do not want to pay.
Myth: Income affects your credit score. Income is not a factor in FICO scoring. A person earning $30,000 with perfect payment history and low utilization can have a higher score than someone earning $300,000 with missed payments and high balances.
Myth: Checking your score lowers it. Checking your own score is always a soft inquiry with zero impact. Only applications for new credit generate hard inquiries.
See how different actions would affect your score. Use the free Credit Score Simulator to model the impact of paying down balances, closing accounts, opening new credit, and other changes — no signup required.
Related tools: Credit Utilization Calculator · Credit Card Payoff Calculator · Debt-to-Income Calculator · Mortgage Calculator