• A measure designed to help student loan borrowers with their payments expired this week, putting some borrowers at risk of delinquency.
• As of Sept. 30, missed payments can be reported to credit agencies.

The one-year grace period for student loan borrowers who miss a payment expired this week. And yet, millions of Americans are likely unprepared to give up that key safety net.

The goal of the 12-month "on ramp" to repayment was to give borrowers some breathing room as they worked student loan payments back into their budgets. Although interest still accrued on their balances, missed payments did not damage their credit.

As of Sept. 30, however, student loan servicers are once again able to report missed payments to credit agencies, which means falling behind could hurt your credit score — that three-digit number that lenders use to determine if you can borrow, and the interest rate you'll pay for credit cards, car loans and mortgages.

Generally speaking, the higher your credit score, the better off you are when it comes to getting a loan.

Recent studies show some borrowers are at risk of not being able to keep up.

Some borrowers haven't made payments in years

Congress initially passed legislation to allow federal student loan borrowers to pause their loan payments in March 2020 as part of the Covid economic response. During that time, interest rates on most federal loans were set to zero. It's now been roughly a year since student loan payments resumed.

Almost half, 47%, of borrowers said they've made at least some payments since the end of the payment pause, but 26% said they made no payments at all, according to a new report by the National Endowment for Financial Education. The nonprofit in August polled 813 adults who have or had student loan debt.

"When you have to cut $500 to $1,000 from the monthly budget, that's a significant amount of dollars people don't have for other things," said NEFE president and CEO Billy Hensley, a member of the CNBC Global Financial Wellness Advisory Board. "This will continue to be a shock and reverberate around the kitchen table."

A separate report by Intuit Credit Karma also found that 20% of student loan borrowers have not made any payments toward their student loans since the pause ended and the majority — 69% — of borrowers who have not been paying on time said they will not be able to afford to pay down the interest they've accrued.

Many of those borrowers are now worried their credit score will take a hit once their student loan payment history is reported to the credit bureaus, Credit Karma found. In August, the site surveyed nearly 2,000 adults with outstanding student loan debt.

Consequences could be 'catastrophic'

"When you don't pay something for 4½ years the intent is clear, you are not going to pay," said certified financial planner Ted Jenkin, CEO and founder of oXYGen Financial in Atlanta, referring to the pandemic-era pause on federal student loan payments.

"Many believe that someone is going to bail them out and I think it's going to end badly for a lot of people," said Jenkin, who is also a member of CNBC's Financial Advisor Council.

In fact, 48% of student loan borrowers anticipate debt forgiveness in the future, according to Sallie Mae's annual How America Pays for College report. Of those who expect forgiveness, 37% plan to work in public service, while 7% say their future employer will pay for their loans. The biggest share, 47%, think the government will forgive student loans.

While there are still opportunities for relief, missed payments could now come at a high cost for borrowers, Jenkin said. "It's going to be catastrophic to their credit score."

How a missed payment can hurt your credit score

Student loan delinquencies will show up on your credit report once they hit 90-days past due, according to Liz Pagel, senior vice president of consumer lending at TransUnion.

"If a consumer misses their October payment and still hasn't made the payment in November or December, then in January they will be reported as 90-days past due for that October payment and that is when their credit will be negatively impacted," she said.

TransUnion data shows that just over half of student loan borrowers made payments over the past several months. 

"That doesn't necessarily mean that these consumers cannot make the payments," Pagel said. "Some may have made a logical choice to hold off awaiting possible loan forgiveness or just because they were aware that their credit would not be affected by not making payments."

More from Personal Finance:
Federal judge extends block on Biden's student debt forgiveness plan
The sticker price at some colleges is now nearly $100,000 a year
These are the top 10 highest-paying college majors

To be sure, working those payments back into budgets after a four-year hiatus may require some sacrifices.

In the last year, roughly three-quarters of borrowers with student loan balances have had to make budgetary changes in order to make their payments, according to the NEFE report.

"If you don't want your credit rating impacted, you have to develop a budget and figure out how you are going to incorporate student loan payments into that budget," said Andrew Housser, co-founder and co-CEO of personal finance site Achieve.

"It's crucial to look at options for consolidating other debts and reducing interest rates where possible," Housser explained.

Of those with outstanding loans, 31% said they are less likely to pursue additional education, after taking the end of the repayment pause into account, NEFE also found.

A separate study commissioned by EdAssist by Bright Horizons also highlighted the impact student loan debt has had on borrowers.

To that point, 53% of U.S. workers said that knowing they would incur additional debt has prevented them from pursuing more education.

And as much as 86% of workers with education debt said their degree wasn't worth the toll that student loans has had, according to Bright Horizons' fourth annual education index, which in May polled more than 2,000 adults who are employed either full- or part-time.

Consumer advocates often caution students not to borrow more than you expect to earn as a starting salary.

"Higher education needs to do a better job of helping people understand the earning potential of a degree," said NEFE's Hensley. "We need to talk through how to launch and what that plan looks like."

Subscribe to CNBC on YouTube.