The U.S. wars in Afghanistan and Iraq will cost American taxpayers $4 trillion to $6 trillion, taking into account the medical care of wounded veterans and expensive repairs to a force depleted by more than a decade of fighting, according to a new study by a Harvard University researcher.

Washington increased military benefits in late 2001 as the country went to war, seeking to quickly bolster its talent pool and expand its ranks. Those decisions and the protracted nation-building efforts launched in both countries will generate expenses for years to come, Linda Bilmes, a public policy professor, wrote in the study released Thursday.

“As a consequence of these wartime spending choices, the United States will face constraints in funding investments in personnel and diplomacy, research and development and new military initiatives,”the report says. “The legacy of decisions taken during the Iraq and Afghanistan wars will dominate future federal budgets for decades to come.”

Bilmes said the United States has spent almost $2 trillion already on the military campaigns in Afghanistan and Iraq and those costs, she said, are only a fraction of the ultimate price tag. The biggest ongoing expense will be providing medical care and disability benefits to veterans of the two conflicts.

“Historically, the bill for these costs has come due many decades later,” the report says, noting that the peak disbursement of disability payments for U.S. veterans in the last century came decades after the conflicts ended. “Payments to Vietnam and first Gulf War veterans are still climbing.”

Spending borrowed money to pay for the wars has also made them more expensive, the study noted. The conflicts have added $2 trillion to the U.S. debt, representing roughly 20 percent of the debt incurred between 2001 and 2012.

Bilmes’ estimate provides a higher range than another authoritative study on the issue by Brown University’s Eisenhower Research Project. Brown researchers put the price tag at roughly $4 trillion.

Both figures are dramatically higher than what U.S. officials projected they would spend when they were planning to go to war in Iraq. Stephen Friedman, a senior White House official, left the government in 2002 after irking his colleagues by publicly estimating that the Iraq war could end up costing up to $200 billion.

It’s unclear how long Washington will keep paying bills for that conflict, which dragged on for nearly a decade and became deeply unpopular both at home and in Iraq. Judging from history, it could take quite awhile. The Associated Press recently found that the federal government is still cutting checks each month to relatives of Civil War veterans, nearly 150 years after the end of that conflict.