Before you retire, you will know exactly what you'll get each month. Your plan administrator can help you figure it out.
1) Final average earnings: This plan bases your pension on how much you made over your last few years with the company. Often it's the last five years. Some plans take the best five years out of the last 10. The best plans take the best three years out of your last 10.
2) Career average earnings: This plan bases your pension on your average income over your years in the plan. For instance, your pension may equal 1.5% of what you earned on average.