How Credit Scores Actually Work

Here's a truth that costs people money every day: the credit score you check on free apps is probably not the score your lender sees.

Credit Karma shows you VantageScore. Most lenders use FICO. The difference can be 20, 30, even 50+ points. That's the difference between "approved" and "denied," or between a 6% and an 8% interest rate on your car loan.

This guide breaks down exactly how credit scores work — no fluff, no upsells, just the mechanics you need to understand to actually improve yours.

The Two Companies That Score Your Credit

There are only two companies that create the mathematical models used to calculate credit scores:

FICO (Fair Isaac Corporation) — Created in 1989, used by over 90% of top lenders for credit decisions. When a mortgage company, auto dealer, or credit card issuer checks your score, they're almost certainly pulling a FICO score.

VantageScore — Created in 2006 by the three credit bureaus (Equifax, Experian, TransUnion) as a competitor to FICO. Used heavily by free credit monitoring apps and some credit card issuers for account management, but rarely for actual lending decisions.

The 5 Factors That Determine Your FICO Score

FICO doesn't release their exact algorithm (it's a trade secret), but they've published how much weight each factor carries:

1. Payment History (35%)

This is the biggest factor, and for good reason — lenders want to know if you pay your bills. One 30-day late payment can drop a 780 score by 90-110 points. A 90-day late is even worse.

The good news: payments aren't reported late to the bureaus until they're 30+ days past due. If you're a week late, you'll get hit with a late fee from your bank, but your credit score won't be affected.

2. Credit Utilization (30%)

This is your credit card balance divided by your credit limit. If you have a $1,000 limit and a $300 balance, that's 30% utilization.

Common advice says "keep it under 30%." That's wrong — or at least, incomplete. People with 800+ credit scores average 4.1% utilization, not 30%. And counterintuitively, 0% utilization actually hurts your score slightly (by 12-20 points) because it looks like you're not using credit at all.

Read more: Why the 30% Rule Is Wrong →

3. Length of Credit History (15%)

This includes your oldest account, newest account, and average age of all accounts. People with perfect 850 scores have an average oldest account of 30 years.

This is why closing old credit cards hurts your score — and why the authorized user strategy works so well for building credit fast.

4. Credit Mix (10%)

Having different types of credit (credit cards, auto loan, mortgage, student loans) shows you can manage various debt types. But don't open accounts just for mix — it's only 10% and not worth the hard inquiries.

5. New Credit (10%)

Each hard inquiry (from applying for credit) typically costs 2-5 points and stays on your report for 2 years (but only affects your score for 12 months). Opening several new accounts quickly is a red flag to lenders.

Why You Have Different Scores at Each Bureau

You don't have one credit score — you have dozens. Here's why they differ:

Different data at each bureau. Not all creditors report to all three bureaus. If a credit card only reports to Experian, it won't help your TransUnion or Equifax scores.

Different timing. Bureaus receive updates at different times. Your Experian file might show a payment you made yesterday while TransUnion still shows last month's balance.

Different score versions. FICO alone has 28+ scoring models. The "FICO Score 8" that credit cards use is different from the "FICO Score 2" that mortgage lenders use. VantageScore has its own versions.

Which Score Do Lenders Actually Use?

FICO 8 vs FICO 9 vs FICO 10T: What's Different?

FICO 8 (most widely used): Paid collections still hurt your score. Medical debt treated same as other debt.

FICO 9 (newer): Ignores paid collections entirely. Medical debt weighted less heavily.

FICO 10T (newest): Uses "trended data" — it looks at your balance trajectory over 24 months, not just the current snapshot. Someone paying down debt gets rewarded; someone running up balances gets penalized, even if current utilization is identical.

FICO 10T is approved for Fannie Mae/Freddie Mac mortgages as of 2025, so it's finally rolling out after years of delay.

Where to Check Your Actual FICO Score for Free

Don't pay for credit monitoring. Here's how to see real FICO scores free:

• Experian.com — Free FICO Score 8 (Experian data). This is the only free site showing actual FICO.
• Discover Credit Scorecard — Free FICO 8 (TransUnion data), even if you're not a Discover customer.
• Most credit card issuers — Amex, Chase, Bank of America, Citi, and Wells Fargo all provide free FICO scores to cardholders.
• AnnualCreditReport.com — Free credit reports from all three bureaus weekly (permanently, as of October 2023).

Credit Karma is useful for monitoring changes and catching errors, but remember — it's VantageScore, not FICO.

The Bottom Line

Understanding how credit scores work is step one to improving yours. The key takeaways:

1. Payment history and utilization are 65% of your score. Master those two factors.
2. The score you see on free apps isn't what lenders see. VantageScore ≠ FICO.
3. You have dozens of credit scores. They differ by bureau, by score version, and by timing.
4. FICO 8 is still king for credit cards and most loans. Mortgages use older FICO versions.

Ready to actually improve your score? Start with our guide on 7 free methods that work, or use our free credit tools.