A worker whose lifetime average earnings are four times another worker’s does not collect four times the Social Security benefit. The formula is built to prevent that.
Social Security converts a career into a single number first. The Social Security Administration takes the 35 highest-earning years of a worker’s record, indexes each of them to national wage growth, adds them up, and divides by 420 months. The result is Average Indexed Monthly Earnings, or AIME. Everything about the eventual check follows from that one figure.
AIME then runs through a three-bracket formula set out in section 215(a) of the Social Security Act. The percentages have not moved since 1979: 90%, 32%, and 15%. What moves each year are the two dollar thresholds where the rate steps down, which SSA calls bend points. For workers who turn 62 in 2026, the bend points are $1,286 and $7,749. Those two numbers are locked to the year a worker turns 62 and follow that worker for life, regardless of when the benefit is actually claimed.
The formula, applied
The output is the Primary Insurance Amount, the monthly benefit payable at full retirement age, which is 67 for anyone born in 1960 or later. Below, four workers with the same 35-year career length and different earnings histories, run through the 2026 brackets.
| AIME | 90% of first $1,286 | 32% of $1,286–$7,749 | 15% above $7,749 | Monthly PIA | Share of AIME replaced |
|---|---|---|---|---|---|
| $2,000 | $1,157.40 | $228.48 | — | $1,385.88 | 69% |
| $5,000 | $1,157.40 | $1,188.48 | — | $2,345.88 | 47% |
| $9,000 | $1,157.40 | $2,068.16 | $187.65 | $3,413.21 | 38% |
| $13,000 | $1,157.40 | $2,068.16 | $787.65 | $4,013.21 | 31% |
Replacement shares rounded to the nearest percent. The $13,000 worker earned 6.5 times as much per month as the $2,000 worker across a full career. The benefit is 2.9 times larger. The replacement rate falls from 69% to 31% across the same span, and every dollar of that compression comes from the two rate steps.
The steps are steep. A dollar of AIME landing in the first bracket is worth 90 cents of monthly benefit. The same dollar landing above $7,749 is worth 15 cents. That is a six-fold difference in the value of identical earnings, decided entirely by where a worker’s average sits.
What a single good year is worth
The 35-year divisor is the part that surprises people. AIME divides by 420 months no matter what, so one additional year of earnings changes the average by that year’s indexed amount divided by 35 — and only to the extent it displaces a lower year already in the record.
Take a worker at the top of the middle bracket who earns an extra $12,000 in one year, above what that year would otherwise have contributed. AIME rises by $12,000 ÷ 420, or $28.57 per month. At the 32% rate, the monthly benefit rises by $9.14. For a worker already above the second bend point, the same $12,000 raises the benefit by $4.29 a month.
That is the arithmetic behind a common piece of retirement advice being weaker than it sounds. Working one more year at a high salary does move the benefit, but through a divisor of 420 and then through a 32% or 15% rate. The lever is short. The larger levers are elsewhere: claiming later raises the benefit by roughly 8% per year of delay between full retirement age and 70, and that increase applies to the whole PIA rather than to one year’s marginal contribution.
Why the shape is the way it is
The 90% first bracket exists because Social Security is insurance against low lifetime earnings, not a savings account. A worker with an AIME of $2,000 has almost no capacity to have saved separately; the formula replaces more than two-thirds of that income. A worker with an AIME of $13,000 was in a position to accumulate other assets, and the formula replaces less than a third.
The cap reinforces this. Only earnings up to the taxable maximum count, which SSA set at $184,500 for 2026, up from $176,100 in 2025. Income above that line is neither taxed for Social Security nor credited toward AIME, which is why the fourth row of the table is close to the practical ceiling rather than an arbitrary high number. The 2.8% cost-of-living adjustment SSA announced on 24 October 2025 for 2026 payments applies after the formula runs, scaling the finished PIA rather than the brackets that produced it.
The decision
The formula rewards the length of a record far more than the height of any point in it. A worker with 30 years of earnings has five zeros averaged into the 420-month divisor, and filling those zeros with even modest work converts dollars at 90% or 32% instead of 15%. A worker already at 35 solid years faces the flat side of the curve, where an extra $12,000 of earnings buys $4.29 a month.
The math says the second bend point at $7,749 is where additional career earnings stop mattering much. The decision that still matters after that point is timing: 8% a year for delaying past 67 applies to the entire benefit, which for the $9,000 AIME worker is worth about $273 a month per year of delay against the $4.29 a marginal high-earning year would add. Anyone at the top of the third bracket is optimizing the wrong variable by working longer for the earnings record alone.