A new report from the Brown University Costs of War Project estimates that US taxpayers have paid an average of $8,000 each and over $2 trillion total for the Iraq war alone.

The group says the actual costs of war exceed the Pentagon's approved budgets, spilling into other parts of the federal budget.

Unlike most wars in history, the war is financed by borrowing money, which leads to huge interest payments — not to mention increased pay to retain soldiers and medical and disability care.

Aside from the staggering cost of the Iraq War, the group estimates the US has spent over $6.4 trillion total on all of its "War on Terror" efforts.

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The human costs of war are huge and crippling. The financial costs can be, too.

According to a new estimate by the Costs of War co-director Neta Crawford, US taxpayers have paid nearly $2 trillion in war-related costs on the Iraq war alone.

Newsweek estimated that the total for the Iraq War comes out to an average of roughly $8,000 per taxpayer. The figure far exceeds the Pentagon's estimate that Americans paid an average of $3,907 each for Iraq and Syria to date. And in March 2019, the Department of Defense estimated that the wars in Iraq, Afghanistan, and Syria combined have cost each US taxpayer around $7,623 on average.

The Costs of War Project through Brown University conducts research on the human, economic, and political costs of the post-9/11 wars waged by the US. Stephanie Savell, a co-director of the Cost of Wars Projects, told Insider it's important for Americans to understand exactly what their taxes are paying for when it comes to war-related expenses.

"As Americans debate the merits of U.S. military presence in Iraq and elsewhere in the name of the U.S. war on terrorism, it's essential to understand that war costs go far beyond what the DOD has appropriated in Overseas Contingency Operations and reach across many parts of the federal budget," Savell said.

Breaking down the financial costs of the Iraq War

The Pentagon had been allotted approximately $838 billion in "emergency" and "overseas contingency operation" for military operations in Iraq from the fiscal year 2003 to 2019, including operations fighting ISIS in Iraq and Syria. However, Savell says the actual costs of the war often exceed that of the Congress-approved budgets.

"When you're accounting for the cost of war, you can't only account what the DOD has spent on overseas contingency funds," Savell told Insider. "You have to look at the other sets of costs including interest on borrowed funds, increased war-related spending, higher pay to retain soldiers, medical and disability care on post-9-11 and war veterans, and more."

US troops in Iraq. Tech. Sgt. Jeremy T. Lock/US Air Force

According to their estimates, the cost of the Iraq War to date would be $1,922 billion in current dollars — this figure includes funding appropriated by the Pentagon explicitly for the war, spending on the country by the State Department, the care of Iraq War veterans and interests on debt incurred for the 16 years of the US military's involvement in the country.

Crawford says that war-related spending in Iraq has blown past its budget in the 16 years military forces have been in the country, estimating a nearly $382 billion surplus in Iraq alone.

The increases to the Congressionally approved budgets were used to heighten security at bases, for enlistment and reenlistment bonuses, to increase pay to retain personnel, and for the healthcare costs of servicemembers.

A US soldier in Iraq. Getty

Aside from the Defense Department costs, the State Department added approximately $59 billion to the total costs of the Iraq War for USAID on Iraq and Syria. Meanwhile, $199 billion has been spent on Iraq war veterans receiving medical care, disability, and other compensation.

The US has gone deep into debt to pay for the war. That means it has interest payments.

As expected, that taxpayer dollars are going towards war-related expenses including operations, equipment, and personnel. But a surprising amount of the costs are to pay off the interest on the debt the US has accrued since going to war.

"People also need to know that these wars have been put on a credit card, so we will be paying trillions on war borrowing in interest alone over the next several decades," Avell told Insider.

Since the US launched its "Global War on Terror" in Iraq and Afghanistan — and later Yemen, Pakistan, and other areas — the US government has completely financed its war efforts borrowing funds. A Cost of War Projects report estimated the US government debts from all post-9/11 war efforts "resulted in cumulative interest payments of $925 billion" on a $2 trillion debt.

The financing method departs from previous international conflicts, where the federal government either raised taxes or issued war bonds to finance war-related expenses. According to Boston University political scientist Rosella Cappella-Zielinski, tax payments accounted for 30% of the cost of World War I and almost 50% of the cost of World War II.

A US soldier stands while bulldozers clear rubble and debris at Ain al-Asad air base in Anbar, Iraq, Monday, Jan. 13, 2020. AP Photo/Ali Abdul Hassan

Borrowing from both domestic and foreign sources, Crawford estimates the US has incurred $444 billion in interest on borrowing to pay for Pentagon and State Department spending in Iraq alone.

While the money spent on the Iraq War may seem staggering, the Costs of War estimates the US has spent over $6.4 trillion total on all of its "War on Terror" efforts in Iraq and Afghanistan, and the related violence in Pakistan and Syria.

Defense Department spokesperson Christopher Sherwood told Insider that the Defense Department dedicates $1.575 trillion for war-related costs, with an average of spending $4.2 billion per month on all operations for the fiscal year 2019.

Sherwood said that the department's costs go towards war-related operational costs, such as trainings and communications, support for deployed troops, including food and medical services, and transportation of personnel and equipment.

The human costs of the Iraq War are even harder to track

The US invaded Iraq in 2003 on the belief that Saddam Hussein had, or was attempting to make, "weapons of mass destruction" and that Iraq's government had connections to various terrorist groups, including al-Qaeda. Although the invasion initially had overwhelming support from the American public and the approval of Congress, it is now considered one of the greatest foreign policy blunders in US history.

189,000 soldiers were killed in direct war deaths and 32,223 injured, Cost of War estimated. Meanwhile, the deaths of hundreds of thousands of service members due to war-related hardships remain difficult to track.

US Navy Hospital Corpsman HM1 Richard Barnett, assigned to the 1st Marine Division, holds an Iraqi child in central Iraq on March 29, 2003. REUTERS/Damir Sagolj

The Costs of War Project believes calculating the total costs of war — economic, political, and human — is important to ensure that Americans can make educated choices about war-related policies.

"War is expensive — in terms of lives lost, physical damage to people and property, mental trauma to soldiers and war-zone inhabitants, and in terms of money," Cost of War researcher Heidi Peltier wrote.

In 2016 and leading up to 2020, President Donald Trump has campaigned on a promise of pulling American troops out and ending "these ridiculous wars" in the Middle East. However, Trump deployed more troops to the country after an attack on the US embassy in Iraq.

The Pentagon originally requested less than $10 billion of that amount for Operation Inherent Resolve in Iraq and Syria — however, the Crawford believes that budget may be blown after more troops were sent into a war zone that was meant to be winding down.