The amount of money the state of Michigan pays out to public school employees in pension payments has almost quadrupled over the past 20 years.

That’s in part because the number of retirees enrolled in the pension system has almost doubled over a 20-year period. In 1996, there were 107,465 people who collected $1.25 billion in annual benefits. Factoring in inflation, that $1.25 billion would be equal to $1.91 billion in 2016 dollars. Last year, there were 211,007 public school retirees who received $4.67 billion from the state-run pension system. The average annual benefit in 2016 was $22,138.