There is a number that does not appear in your bank account or on your pay stub, but it can influence your access to credit, a mortgage, and sometimes even a rental or a job more than either of them. That number is your credit score.

In the first quarter of 2026, 2.6 million student loan borrowers fell into default in the U.S. Their scores dropped by an average of 91 points almost overnight. That is not an abstract number: it is the difference between qualifying for a mortgage or not. Between paying 5% or 8% interest on a loan. Between getting the apartment or losing it.

Understanding how that number is built is, literally, money.

📊 What the score is and how it is calculated

A credit score is a number between 300 and 850 that summarizes your financial behavior history. The most widely used model in the U.S. is FICO, calculated from five factors with different weights.

The first thing that stands out: 65% of the score depends on just two factors. Paying on time and not using too much of your available credit. Everything else is secondary.

🎯 The ranges: what each score means

A low score does not just close doors: it opens them at a higher price. The difference between a 620 score and a 760 score on a $300,000 mortgage can amount to $100,000 in interest paid over 30 years. Same loan, same bank, same borrower. Only the number changes.

🚀 How to build it from zero

Having no credit history is almost as problematic as having a bad one. Lenders cannot assess the risk of someone without data, and the usual answer is rejection or very high rates.

The most accessible tool to start from zero is a secured credit card: a credit card where you deposit an amount, usually $200 to $500, that works as your limit. You use it for small expenses, pay the full balance every month, and the bank reports that positive behavior to the bureaus. In 6 to 12 months, you already have history.

Other strategies for beginners include becoming an authorized user on a family member’s card with a good history, or using a credit-builder loan, a loan designed specifically to build history where the money stays in a savings account until you finish paying.

⚠️ The mistakes that hurt it the most

Some behaviors have a disproportionately negative impact on your score, and it is worth knowing them before making them by accident.

🛡️ How to protect it

Building a score takes years. Destroying it can take weeks. That is why protecting it is just as important as building it.

The most effective measure against identity theft, which can ruin a score even if you did nothing wrong, is a credit freeze: a free block that prevents any lender from accessing your history to open new credit lines in your name. It can be activated and deactivated in minutes on each bureau’s website.

Reviewing your report at least once a year is also critical. Up to 1 in 5 reports has errors that unfairly lower the score. In the U.S., you have the right to one free annual report from each bureau, Equifax, Experian, and TransUnion, at AnnualCreditReport.com.

Don Roi’s lesson

• 65% of your score depends on two things: always paying on time and not using more than 30% of your available credit.
• The difference between a 620 score and a 760 score can translate into $100,000 in extra interest on a 30-year mortgage.
• Closing old cards may seem organized, but it has two negative effects at the same time: it reduces history length and increases utilization.
• A credit freeze is free, reversible, and the most effective tool to protect your score against identity theft.
• In 2026, 2.6 million people saw their score drop by 91 points because of student loan default. Most did not see it coming because they were not checking their report.

Your score is not a value judgment. It is a snapshot of your financial behavior over time. And like any snapshot, you can change what it shows. You just need to know which factors to move, in what order, and with what consistency. Time does the rest.