Missouri's auditor says the state's $585 million tax credit system needs better oversight and a more accurate means of measuring its benefits.

In an audit released Monday, State Auditor Susan Montee pointed to systematic flaws with how state agencies estimate the economic impact of tax credits.

"When you look at the numbers themselves, there was a $1.1 billion difference between what we expected to spend in that five year period and what we actually did," says Montee. "These are huge, huge numbers."

The audit says Missouri should have tighter controls, such as yearly legislative review, on how money is spent.

The audit comes as lawmakers and the governor are debating whether to modify tax credit programs to help balance future state budgets.

A tax credit reduces the taxes owed by a person or business.

Individuals and businesses redeemed about $585 million in state income tax credits last year, an 86 percent increase since 2000.