Two years ago, the Obama administration pronounced its federal spending tracking system a success, saying it helped save agencies some $5.8 billion in IT-related spending.

The system, known as PortfolioStat, keep tabs on how much the government is spending on its massive IT projects, which have sometimes gone years behind schedule and billions over budget. PortfolioStat is supposed to prevent that – or at least help agencies get a handle on how much they’re actually spending.

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Agencies, however, have been slow to adapt to the new system and apparently have been making errors – leading the government to severely overstate how much it’s actually saved in IT spending.

A new report from the GAO says the savings are actually about $2 billion. That’s 66 percent less than originally estimated.

The GAO blames agencies for inconsistent reporting measures that led to the far-off estimates made by the Office of Management and Budget (OMB).

The auditors said the behemoth Department of Defense had the most errors in reported savings – with the discrepancy totaling about $2.6 billion. The massive difference is likely because the Pentagon stopped tracking its savings in the system, the GAO said.

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DOD officials, for their part, said the Pentagon’s IT systems aren’t capable of generating the data needed to track savings in PortfolioState. They told the GAO the costs of getting their systems to track the savings would “far outweigh any potential benefits.”

The second largest cost-savings discrepancy came from the Department of Homeland Security, where officials told auditors they “mislabeled” their savings figures for 2013 in their records. DHS reported saving $925 million more than it actually did.

The report showed the other government agencies taken together overstated their IT cost savings by $206 million.

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“Inconsistencies in OMB and agencies’ reporting make it difficult to reliably measure progress in achieving PortfolioStat savings,” the GAO report said. Auditors recommend that the government’s chief information officer, Tony Scott, ensure that agencies will accurately report their spending in the future.

The Obama administration has been trying to get a handle on tracking the sprawling IT costs within the federal government. Major IT projects have soared millions of dollars – sometimes billions – over budget. The most notable was HealthCare.gov, Obamacare’s federal portal that was riddled with tech glitches in the first few months of its launch.