Checking your credit report regularly is a basic rule of personal finance. More than one in three Americans has failed to follow that rule — they’ve never looked at their report, according to a new study from Bankrate.com.

The report finds that 35 percent of all Americans have never reviewed their credit reports, and 14 percent check less than once a year. Senior citizens are the biggest slackers, with 44 percent saying they’ve never checked their report, followed by 41 percent of millennials.

Related: 5 Easy Ways to Ruin a Perfect Credit Score

Your credit report is the foundation of your credit score, a key number that landlords, employers and lenders use to measure financial responsibility. Having a good credit score is critical for financial success because it gets you access to lenders’ best rates and terms, which can save you thousands of dollars each year.

By law you are entitled to access your credit reports from each of the three major credit-reporting companies — Experian, TransUnion and Equifax — for free once every 12 months. You can do that at AnnualCreditReport.com.

The Bankrate survey found that about half of Americans have reviewed at least one of their credit reports within the past year, and a quarter of Americans review them more than once a year.

“Monitoring your credit goes well beyond scanning a three-digit number,” Bankrate credit card analyst Jeanine Skowronski said in a statement. “Americans need to thoroughly review their credit reports for errors or signs of fraud. They also need to understand what factors, like missed payments or high debt-to-credit ratios, are driving their credit score in order to improve it.”

If you don’t know what’s on your credit reports, now is a good time to find out.