Montana MPERA Retirement Calculator: How to Use It
The calculator follows MPERA's PERS Member Handbook (Rev. 02/2026) for the Defined Benefit Retirement Plan. It doesn't cover the PERS Defined Contribution plan or the public safety systems.
The inputs
Hire date
Before or after July 1, 2011 sets the formula, the HAC period and the retirement ages. July 1, 2007 and July 1, 2013 set the GABA rate.
Highest average compensation
Your highest 36 (pre-2011 hires) or 60 consecutive months of pay, averaged. Enter it as a yearly figure; the calculator divides by 12.
How the result is built
Monthly benefit = factor x service x monthly HAC, using the factor for your total service. For early retirement the calculator stops there and flags it, because MPERA's early retirement factors aren't published. The GABA projection compounds at your rate (the 1.5% maximum for post-2013 hires).
Frequently asked questions
Is there a Rule of 80?
No. Pre-2011 hires: 60 with 5 years, 65 while employed, or 30 years. Post-2011 hires: 65 with 5 years or 70 in active service.
Does the GABA compound?
Yes. Each January's increase applies to the benefit paid the preceding January.
Why is my early retirement amount unreduced?
MPERA applies an actuarial early retirement factor it doesn't publish. Ask MPERA for the reduced figure.
What GABA do post-2013 hires get?
Between 0% and 1.5%, set each year from the plan's funded ratio and amortization period.