The Core Mental Math
The pension formula in plain English: take your years of service, multiply by your multiplier percent, then multiply by your annual salary, and divide by 12 for monthly income. Quick shortcut: at 2.0%, each year of service is worth about 2% of your monthly salary. At 30 years, that’s 60% of your monthly salary. If you earn $5,500/month gross and have 30 years at 2.0%, your pension is roughly 60% × $5,500 = $3,300/month.
Quick pension mental math — 2.0% multiplier shortcuts for common career lengths
| Quick Formula | At 2.0% Multiplier | Example ($6K/mo salary) |
|---|---|---|
| 20 years pension | 40% of monthly salary | 40% × $6,000 = $2,400/mo |
| 25 years pension | 50% of monthly salary | 50% × $6,000 = $3,000/mo |
| 30 years pension | 60% of monthly salary | 60% × $6,000 = $3,600/mo |
| 35 years pension | 70% of monthly salary | 70% × $6,000 = $4,200/mo |
| At 2.5% multiplier | Multiply by 1.25 | 30 yrs: 75% × $6,000 = $4,500/mo |
Quick Tests for Key Decisions
- Should I take early retirement? Multiply the monthly reduction by 12 months × your remaining life expectancy. If leaving 2 years early costs $200/month for 25 years, that’s $60,000 total cost. Does 2 extra years of freedom worth $60,000 to you?
- Is this job change worth it? Multiply the monthly pension you’d forfeit by 12 × expected retirement years. If leaving costs a $1,000/month pension and you expect 25 years of retirement, that’s $300,000 in lifetime value the new job must compensate.
- Should I buy service credit? Divide the purchase cost by monthly benefit gained. $25,000 ÷ $150/month more = 167 months (14 years) to break even. If you expect to live 20+ years in retirement, it’s worth it.
- Is my replacement rate good? Divide your monthly pension by your current take-home monthly pay. If pension = $3,200 and take-home = $5,500, replacement rate is 58% — add Social Security to see total picture.
- How much supplemental savings do I need? Take your monthly income gap × 300 (25 years × 12 months). If gap is $800/month, target $240,000 in savings.
Multiply your annual income gap (how much your pension falls short of your goal) by 25 to get your supplemental savings target at a 4% withdrawal rate. A $12,000/year gap requires $300,000 in savings. This is a quick sanity check you can do in your head.
Confirm Your Mental Math With Exact Numbers
After estimating with back-of-envelope math, run the precise calculation to confirm your retirement date and income projections.