The Iran war could end up costing U.S. taxpayers far more than official figures suggest, according to the analysis of one Harvard academic.

The first 6 days of the the joint U.S.-Israeli operation against the Islamic Republic, beginning February 28, racked up costs of $11.3 billion, according to the Pentagon’s briefing to Congress.

And, while a fragile ceasefire is still in place, efforts to reach a lasting settlement have so far proved elusive, with U.S. forces starting a blockade of Iranian ports on Monday after peace talks over the weekend failed.

“I am certain we will reach $1 trillion for the Iran war.” said Professor Linda Bilmes, public policy expert at the Harvard Kennedy School, in an internal interview.

Her research, published two days before the temporary ceasefire announcement on April 8, identified several reasons why this military operation could have catastrophic consequences for the U.S. national debt well into the future.