Three digits. That's what decides the interest rate on your mortgage, whether you get approved for a lease, and sometimes whether you get hired. Your credit score affects hundreds of thousands of dollars in lifetime borrowing costs, and yet most people only vaguely understand how it works. I've built several credit-related calculators for this site, and the research behind them changed how I think about the whole system. Here's how FICO scoring actually works, what moves the number, and what doesn't — based on data from FICO, Experian, and the CFPB.
About 90% of U.S. lenders use FICO scores, which are calculated from five categories of data pulled from your credit reports at Equifax, Experian, and TransUnion. Each category has 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.
Payment history and utilization together make up 65% of your score. That means the two most impactful things you can do are dead simple: pay on time, keep balances low. Everything else is a supporting detail.
This is the big one. FICO looks at whether you've paid all credit accounts on time — credit cards, installment loans, mortgages, retail accounts, everything with a payment due date.
How late payments hit you: The damage depends on how late, how recent, and how many. A 30-day late is bad; 60 days is worse; 90+ is severe. According to FICO's own data, a single 30-day late payment can drop a 740+ score by 60–110 points. That's not a typo. One missed payment, and months of good behavior evaporate. Multiple lates are worse, but not proportionally — the first one does the most damage.
The 30-day line is everything. Miss your due date by a few days and you'll eat a $25–$40 late fee, but most creditors don't report to the bureaus until you're 30+ days past due. So a payment that's 5 or 15 days late costs you a fee but probably won't touch your score. Cross that 30-day mark though, and the damage is immediate and significant.
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.
Utilization is simply your credit card balance divided by your credit limit. FICO calculates this both per card and across all cards combined — and both numbers matter.
| 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 |
Here's the most useful thing I can tell you about utilization: it has no memory. Unlike payment history (where a late payment haunts you for years), utilization is a snapshot of right now. Drop from 60% to 8% in a single billing cycle and your score reflects the improvement immediately. That makes this the fastest lever available for boosting your score. The Credit Utilization Calculator can show you exactly where you stand and what different paydown amounts would do.
One counterintuitive detail: 0% utilization across all cards actually scores slightly worse than 1–9%. The model wants to see you actively using credit responsibly, not avoiding it entirely. The sweet spot is a small balance reported to the bureaus each month that you then pay in full.
FICO looks at your oldest account, your newest account, and the average age across all of them. Longer history scores better because it gives lenders more data to judge your track record.
This is why you should almost never close your oldest credit card, even if it's collecting dust. Closing it eventually removes the account from your average age calculation and reduces your total available credit (which bumps up utilization). If there's no annual fee, keep it open. Throw a streaming subscription on it and set up autopay.
If you're young and building credit, this factor simply works against you. There's no hack — time is the only way to lengthen your credit history. One legitimate shortcut: getting added as an authorized user on a parent's long-standing card can help, since the card's full history may show up on your report.
FICO likes to see that you can handle different types of credit. The two main categories: revolving credit (credit cards, HELOCs) and installment credit (mortgages, auto loans, student loans, personal loans).
Having only credit cards isn't as strong as having credit cards plus an installment loan. But this is only 10% of your score, so never take out a loan you don't need just to diversify your mix. The scoring bump is way too small to justify paying interest on a loan that serves no other purpose.
Every time you apply for credit, the lender pulls a hard inquiry on your report. Each one can ding your score by about 5–10 points and stays on your report for two years (though FICO only counts the last 12 months in scoring).
Rate shopping exception: FICO understands that comparing rates for a mortgage, auto loan, or student loan is smart, not risky. Multiple hard inquiries for these loan types within a 14–45 day window (varies by FICO version) count as a single inquiry. So you can get quotes from five mortgage lenders in two weeks and it only counts once. Take advantage of this — it exists specifically to encourage comparison shopping.
This exception does not apply to credit cards. Five credit card applications in a month means five separate hard inquiries and a noticeable score hit.
The real cost of credit scores shows up in interest rates. Here's what different score ranges actually mean in dollars:
| 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 difference between a 760 and a 620 on a $350,000 mortgage: about $250/month and $80,000+ over the life of the loan. The same pattern plays out on auto loans, credit cards, and even insurance premiums in some states. Dollar for dollar, improving your credit score is one of the highest-return financial moves you can make.
Pay down credit card balances. Dropping utilization from 50% to under 10% can boost your score by 50–100+ points in a single billing cycle. Fastest lever available, period. If you can't pay everything down at once, focus on the card with the highest individual utilization percentage first.
Dispute errors on your credit report. The FTC found that roughly one in five consumers has a verified error on at least one credit report. That's 20% of people walking around with wrong information dragging down their scores. Common errors: accounts that aren't yours, incorrect balances, late payments that were actually on time. Dispute directly with each bureau through their online portals — it takes 15 minutes and could be worth dozens of points.
Get current on everything. If you have any accounts past due right now, bringing them current stops the bleeding. The damage from previous lates stays on your report, but at least you stop racking up additional negative marks.
Request a credit limit increase. If you've been paying on time, call your card issuer and ask for a higher limit. It instantly drops your utilization percentage without you paying down a cent. Some issuers can do this as a soft inquiry (no score impact), others pull a hard inquiry — ask which it'll be before they run it.
Stop applying for new credit. Every application adds a hard inquiry and lowers your average account age. If you're planning a major purchase like a home or car, freeze the credit card applications for at least 6–12 months beforehand.
Keep old accounts open. Your oldest card anchors your credit history length. Even if you never use it, keep it active with a small recurring charge to prevent the issuer from closing it for inactivity.
Consider an installment loan if you only have cards. Adding a small credit-builder loan or personal loan diversifies your credit mix. But only if you need it for another reason — paying interest just to move a 10%-weighted scoring factor rarely makes financial sense.
Myth: Carrying a balance helps your score. False. Paying in full every month gives you perfect payment history and low utilization. Carrying a balance just costs you interest with zero scoring benefit. I'm not sure where this myth started, but it won't die.
Myth: Closing unused cards helps your score. Almost always the opposite. Closing a card reduces your total available credit (pushing utilization up) and eventually removes the account from your average age calculation. Only close a card if the annual fee isn't worth keeping it.
Myth: Income affects your score. It doesn't. Income is not a FICO factor at all. Someone earning $30,000 with perfect payment history and low utilization can easily outscore someone making $300,000 who's missing payments and carrying high balances.
Myth: Checking your score lowers it. Nope. Checking your own score is always a soft inquiry with zero impact. Check it as often as you want. Only applications for new credit trigger 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