How Social Security Benefits Are Calculated: The Formula
Your Social Security benefit is not based on your last or best salary. It is built from your 35 highest-earning years, indexed for wage growth, run through a formula that replaces a larger share of income for lower earners — and then permanently adjusted up or down by the age at which you claim.
The 35-year rule and the bend points
The SSA averages your best 35 years of indexed earnings into a monthly figure (AIME), then applies bend points: 90% of the first slice, 32% of the middle slice, 15% above that. That progressive formula is why the system replaces roughly 55% of income for a low earner and about 28% for a high earner. Work fewer than 35 years and the missing years enter as zeros — a 30-year career carries five zero years in the average, which is why late-career years of work sometimes replace early low or zero years and raise the benefit more than expected.
Claiming age: the 76% swing
Claiming at 62 instead of full retirement age (67 for those born in 1960 or later) cuts the benefit by about 30%, permanently. Waiting to 70 adds delayed retirement credits of 8% per year past full retirement age — a benefit about 76% larger than the age-62 amount. The break-even for waiting is typically the early-to-mid 80s: live past it and waiting wins by an increasing margin. Health, a spouse's benefit, and whether you keep working before full retirement age (the earnings test can temporarily withhold benefits) all belong in the decision — it is insurance against a long life more than an investment to maximise.
- A spousal benefit can reach 50% of the worker's full-retirement amount; survivor benefits reach up to 100%.
- Benefits are taxable on up to 85% of the amount, depending on combined income.
- Check your earnings record at ssa.gov — unreported or mis-credited years directly cut the benefit.
Questions, answered
Will Social Security run out?
Trust-fund projections show a shortfall in the mid-2030s that would cut scheduled benefits by roughly a fifth if Congress does nothing. Payroll taxes would still cover the majority of benefits — planning with a haircut is prudent, planning on zero is not supported by the projections.
Can I claim and keep working?
Yes. Before full retirement age, earning above the annual limit temporarily withholds $1 of benefits per $2 earned above it (the withheld amounts are credited back later). After full retirement age there is no limit.
Reviewed by Tahir Shehzad, ACMA. Figures are reviewed against the sources on our methodology page. This guide is education, not personal financial advice.