LINCOLN, Neb. — The state prison system has estimated its sentencing screw-up will cost the state $4 million over the next decade, and another $6 million the next four decades, but the senator who requested the estimate believes that’s a lowball figure.

Last month, the Omaha World-Herald reported the state prison system has been incorrectly calculating sentences, letting prisoners out too early and disregarding 2002 and 2013 state Supreme Court sentencing rulings. Prison employees didn’t require inmates to serve their mandatory sentence before earning “good time,” which basically cuts their sentences in half.

Prison officials began recalculating sentences of prisoners with mandatory minimum sentences, and Corrections Director Michael Kenney said in his letter to lawmakers those recalculations resulted in 567 inmates getting longer sentences. But he said many of those revised sentences will have no impact on the department because while the prisoner might get another 10 years tacked onto his sentence, he would have been 215 years old by then.