In May, Department of Health and Human Services (HHS) Secretary Sylvia Burwell testified to Congress that costs for building HealthCare.gov were $834 million. New research from Bloomberg Government suggests that Burwell’s estimate represents a low-end estimate.

According to the new report, spending for HealthCare.gov has been an estimated $2.14 billion. Burwell’s estimates did not include numerous costs related to the project. For instance, she did not include the contract costs for processing paper applications, which are used as a backup. That contract cost $300 million.

Burwell’s figure also does not include spending at the IRS and other agencies related to ACA requirements. For instance, the IRS is required to provide real-time interfacing with HealthCare.gov to verify income and family size for insurance subsidy calculations. Those requirements cost $387 million.

Bloomberg also includes $400 million in costs that were excluded by HHS using creative accounting. When it wrote the ACA, Congress did not appropriate money to HHS for the construction of a federal exchange. Instead, it provided unlimited grants to states to construct their portals. When many states refused to construct their exchanges, HHS was forced to develop HealthCare.gov, but without a dedicated source of funding. HHS said it would need to “get creative” about funding options, leaving many wondering where HHS would eventually get the money. According to Bloomberg, HHS shifted money around to finance the construction of HealthCare.gov, using a number of existing contracts to finance the website’s construction.

Finally, Bloomberg included $255 million more in costs than Burwell due to time period differences. Burwell’s costs were as of February 2014. Bloomberg included costs until August 20, 2014, and then projected the current level of spending forward to the end of the fiscal year, September 30th. But this means that their figures are likely conservative too because federal agencies often ramp up spending— particularly contract spending—as it closes out its fiscal year.

Implementing the ACA is a costly exercise; Bloomberg says the $2.14 billion for HealthCare.gov administration is only a small part of the full $73 billion costs of Obamacare since its passage in 2010. But the administration nonetheless owes taxpayers an accurate accounting for the costs of the system.