The White House and the Mall seen from the Hay-Adams Hotel in Washington. (Oliver Contreras for The Washington Post)

The price tag on a popular student loan repayment program is far larger than Education Department estimates, the Government Accountability Office said Wednesday. The GAO pegged the true cost at about $108 billion and called the Education Department’s accounting unreliable.

To help people manage their student loans, the Obama administration has expanded programs that cap monthly payments to a percentage of earnings and eventually forgives the balance. Enrollment in these income-driven repayment plans is soaring and so is the cost, but the government’s budget estimates are not keeping pace, an oversight that fuels criticism of a federal policy that conservatives say has become far too expensive.

Current budget estimates for income-driven plans are more than double what was originally expected for loans made in fiscal 2009 through 2016, climbing from $25 billion to $53 billion, according to the GAO report. The growth is primarily a result of the rising volume of loans in the plans, but researchers at the GAO say faulty projections from education officials may cause costs to be over- or understated by billions of dollars.

“Some uncertainty is unavoidable when anticipating long-term loan costs,” the GAO wrote, “but we found numerous shortcomings in Education’s estimation approach and quality control practices that call into question the reliability of its budget estimates and affect the quality of information Congress has to make informed budget decisions.”

The report takes issue with education officials’ assumption that borrowers’ incomes will not grow with inflation, which could lower estimated costs by more than $17 billion. The model also fails to account for people switching in or out of the plans in the future, which frequently happens when they have to certify their income to remain in the program each year.

In a letter to the GAO, Amy McIntosh, a deputy assistant secretary in the Education Department, said the agency has been working with Treasury to revise its estimates and agreed that there is room for improvement. The department in its annual budget report said the money being repaid through other student loan programs offsets some of the expense of the income-driven plans.

“The life cycle of a student loan is exceedingly complex, with a multitude of projection paths and outcomes,” McIntosh wrote. “We are constantly seeking to enhance and refine our cost estimation models.”

Still, she noted that the decisions made, and critiqued in the report, were “based on existing staff and system resources available, assessed impact and consideration for conservatism.” The observation calls into question whether the government agency is capable of managing a multibillion-dollar program that is projected to grow.

“Reading between the lines of the GAO report makes it sound like the Department of Education … has got one or two staff with a 30-year-old computer or maybe index cards trying to figure out costs,” said Jason Delisle, a resident fellow at the American Enterprise Institute, a conservative think tank. “You need to hire a firm that is skilled at estimating the value of financial securities to tell you what these loans are worth and what they’ll cost taxpayers.”

As it stands, there are 5.3 million people enrolled in an income-driven repayment plan with about $353 billion in outstanding student loans. Although the government has let people repay education debt based on their income for the past 20 years, few took advantage until the Obama administration expanded the number of options and eligibility. Plans are designed to prevent borrowers from defaulting on their loans and ruining their credit.

“This is a way that we can ensure that graduates are fulfilling their basic responsibility to repay the government for the money that they borrowed,” White House press secretary Josh Earnest told reporters Wednesday. “But we want to make sure that when students graduate, that they’re not saddled with so much debt that they’re essentially penalized financially for pursuing college education opportunities.”

The GAO estimates that $215 billion, or 61 percent of the debt in income-driven plans, will be paid in full. Another $108 billion will be forgiven, with the remaining $29 billion discharged because of death or disability. But those estimates are only for loans made from 1995 to 2017. As more people sign up, the cost of the program will soar.

“At a time when our nation is facing a mammoth national debt, the Department of Education has expanded a student loan program that will cost twice as much as originally estimated,” Senate Budget Committee Chairman Mike Enzi (R-Wyo.), who requested the GAO study, said in a statement. “This administration has been manipulating the terms of the student loan program without the consent of Congress, while shirking its statutory duty to carefully assess the cost impact of those changes.”

Enzi said at the very least there needs to be greater transparency in the way education officials calculate costs, but his office said he is not calling for any major changes to the repayment plans at the moment.

Congressional Republicans have called President Obama’s expansion of the repayment program fiscally irresponsible and pushed for dialing back eligibility. Even Obama has proposed limiting forgiveness for graduate students. Yet President-elect Donald Trump has said he would lower the period of repayment, a move that will probably raise the cost for taxpayers.

“As the Trump administration comes into power they need to take a measured approach that develops a program that is well targeted to the neediest borrowers,” said Michelle Asha Cooper, president of the Institute for Higher Education Policy. “Regardless of who’s in power, the issue of college affordability is a real problem, and while these plans are helpful, they are not a solution.”

Want to read more about the student loans? Check out these stories:

A guide to paying off your student loans

Student debt relief scams are on the rise. Here’s how this government official plans to stop it.

The Obama administration’s plan to lower the student debt payments of millions more Americans