The pension system for thousands of Illinois teachers is officially lowering the forecast of how much money it will make on investments.

Instead of assuming an 8.5% rate of return, the Teachers' Retirement System will now base its plans and projections on 8% growth.

The prediction of less money in the future means the retirement system faces a bigger funding problem. The latest estimate is that TRS has only 42.4% of the money it needs for pensions in the decades ahead.

The retirement system's executive director says assuming a lower rate of return is the prudent thing for long-term planning.

The change also means the state's annual contribution to the pension fund will increase slightly next year.