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How Social Security Benefits Are Calculated
Social Security looks opaque because it runs on three formulas in sequence. Once you see them, every claiming decision gets easier to model.Step 1: Average Indexed Monthly Earnings (AIME)
The system takes your 35 highest earning years, adjusts older years upward for wage inflation, averages them, and divides by 12. Work fewer than 35 years and zeros fill the gaps — each zero drags the average down hard. Working two extra years at $50,000 to replace two zero years can raise the benefit by a noticeable amount even late in a career.
Step 2: The Benefit Formula (PIA)
Your primary insurance amount — the check at full retirement age — applies three replacement rates to AIME with "bend points" that change annually: 90% of the first band, 32% of the middle band, 15% above. The steep first tier is why low earners replace a much larger share of income than high earners.
Step 3: Claiming Age Adjustments
Claiming before full retirement age (67 for anyone born 1960 or later) cuts the check by about 5/9 of 1% per month for the first 36 months, then 5/12 of 1% after — roughly 30% less at age 62. Delaying past FRA adds 8% per year in delayed retirement credits until 70, roughly 24% more. From 62 to 70 the swing between earliest and latest claiming is therefore about 77% in monthly dollars.
What Adjusts Your Check After That
Benefits get a yearly cost-of-living adjustment. Earnings above the annual limit before FRA temporarily withhold part of the benefit; income taxes may apply above combined-income thresholds; and Medicare Part B premiums are deducted from the check once enrolled.
A Worked Sketch
Take a worker with an AIME of $6,000. Using a recent year's bend points ($1,200 and $7,200 as a shape, not exact figures): 90% × $1,200 = $1,080; 32% × $4,800 = $1,536; 15% × $0 = 0. PIA ≈ $2,616 per month at FRA. Claim at 62 and it is roughly $1,830; wait until 70 and roughly $3,240. Same career, same record — the claiming date alone moves the check by $1,400 a month.
Your own numbers live on your statement at the official website; the formulas above tell you how to stress-test them.
This article is general educational information only, not financial, tax, investment, accounting, or legal advice, and is not a recommendation to buy, sell, or hold any product or security. Figures reflect published IRS, HMRC, and Social Security Administration guidance for 2026 and are subject to change and annual indexing; always confirm current thresholds with the official source before acting. Rules differ by country, state, and personal situation, and nothing here creates a fiduciary or advisory relationship. This site is supported by advertising, which does not influence our editorial conclusions. For any decision with real financial consequences, consult a licensed fiduciary advisor or tax professional.