Social Security Benefit Calculation

How it works

Social Security benefits are based on your Primary Insurance Amount (PIA), which is your benefit at Full Retirement Age (FRA). Claiming early reduces benefits permanently, while delaying increases them permanently. Stratum determines the benefit amount for each person using a three-way priority: (1) a manual Social Security income entry in the income table wins outright, (2) if no manual entry exists and wage income is present, Stratum auto-estimates using the SSA bend-point formula (wages → AIME → PIA → benefit adjusted for claiming age), and (3) the SS Optimization strategy can override the claiming age and optionally the PIA for auto-calculated persons.

1. 1. Determine Full Retirement Age (FRA)

   FRA depends on birth year

   Born 1943-1954: Age 66
   Born 1955: Age 66 and 2 months
   Born 1956: Age 66 and 4 months
   Born 1957: Age 66 and 6 months
   Born 1958: Age 66 and 8 months
   Born 1959: Age 66 and 10 months
   Born 1960+: Age 67

   Example: Client born 1965 → FRA is age 67

2. 2. Build the Year-by-Year Earnings History

   Reconstruct an estimated wage for every year in the 35-year window, then cap each year at that year's Social Security wage base

   For each year Y from (tax year − 34) through the claim year:
   
   Estimated wage(Y) = entered wage × (1 + rate)^(Y − anchor year)
     - Years BEFORE the entered wage's anchor year use the scenario inflation rate
     - Years AFTER use the wage item's own indexing rate (0% when wage indexing is off)
     - Wage items with an explicit start/end year contribute only inside that window
   
   Credited wage(Y) = min(Estimated wage(Y), SS wage base(Y))
   
   The wage base is the SSA-published historical value for past years, and the latest published base projected forward at inflation for future years.

   Example: $200,000 entered for 2026 with 2.5% inflation → estimated 1990 wage of $82,200, capped to the published 1990 wage base of $51,300. Every year is capped against its own base, in that year's nominal dollars.

3. 3. Index Earnings and Calculate AIME

   Restate each year's credited wage in FRA-year dollars, then average the highest 35

   Indexed wage(Y) = Credited wage(Y) × (1 + inflation)^(FRA year − Y)
   
   AIME = (sum of the 35 highest indexed wages) ÷ 35 ÷ 12
   
   If fewer than 35 years are available, the sum is still divided by 35 — matching SSA's treatment of zero-earnings years.

   Example: 35 indexed years totaling $4,200,000 → AIME = $4,200,000 ÷ 35 ÷ 12 = $10,000/month

4. 4. Apply the Bend-Point Formula (PIA)

   Convert AIME to the Primary Insurance Amount using SSA's three-tier progressive formula

   PIA = 90% × min(AIME, BP1)
       + 32% × min(AIME − BP1, BP2 − BP1)
       + 15% × max(AIME − BP2, 0)
   
   Bend points BP1 and BP2 are the SSA-published values for the scenario's tax year, scaled to FRA-year dollars at the inflation rate — the same rate used to index the earnings. Because AIME and the bend points are scaled together, the result does not depend on which year is chosen as the anchor.

   Example: The formula is deliberately progressive: the first dollars of AIME are replaced at 90%, the last at 15%. High earners therefore see a much lower replacement rate than low earners.

5. 5. Calculate Early/Late Claiming Adjustment

   Benefits adjust based on how far from FRA you claim

   Early (before FRA):
   - Reduce 5/9 of 1% per month for first 36 months (6.67% per year)
   - Reduce 5/12 of 1% per month beyond 36 months (5% per year)
   
   Late (after FRA):
   - Increase 2/3 of 1% per month (8% per year) up to age 70

   Example: FRA 67, claim at 62 (5 years early): -30% reduction FRA 67, claim at 70 (3 years late): +24% increase

6. 6. Calculate Monthly Benefit

   Apply the claiming adjustment to PIA, then grow from FRA-year dollars to claim-year dollars

   Monthly Benefit = PIA × (1 + Adjustment %) × (1 + COLA)^(claim year − FRA year)
   
   Adjustment % ranges from -30% (age 62) to +24% (age 70).
   
   The PIA is expressed in FRA-year dollars, so the COLA factor restates it in the dollars of the year benefits actually begin. Claiming before FRA discounts back; claiming after FRA grows forward.

   Example: PIA $3,000 (FRA year 2040), claim at 62 in 2035 → $3,000 × 0.70 × (1.024)^-5 = $1,865/month in 2035 dollars

7. 7. Calculate Annual Benefit

   Monthly benefit times 12, prorated in the first year for the claiming month

   Annual Benefit = Monthly Benefit × 12
   
   Claim-year benefit = Annual Benefit × (months collected ÷ 12)
   
   SSA begins payments in the month the beneficiary reaches the claiming age, so the first year is partial when the birthday falls mid-year. Months collected = 13 − birth month. Every year after the claim year pays the full annual amount, grown by COLA. When no birth month is recorded, a full 12 months is assumed.
   
   This birth-month proration applies to ESTIMATED and OPTIMIZED benefits, where Stratum knows the claim year. A manually entered Social Security amount is NOT prorated automatically — an entered figure is just as likely to be a benefit already in payment as one about to begin, and Stratum cannot tell the difference. When an entered benefit starts mid-year, set 'Months in First Year' on that income item (Base Data → Income → item info modal) to the months that will actually be collected.

   Example: $2,100/month with a July birthday → $25,200 annual, but the claim year pays $25,200 × 6/12 = $12,600. For an entered benefit of $25,200 first paid in July, set Months in First Year = 6 to get the same result.

Real-world context

What drives the result

Assumptions

• Benefit amount determined by priority: (1) manual social-security income entry in the income table — Stratum uses this directly and skips auto-calculation; (2) auto-estimated from wage income using the SSA bend-point formula (AIME → PIA → claiming-age adjustment); (3) SS Optimization strategy claiming age and optional PIA override applied when active and no manual entry exists
• A manually entered benefit is assumed to be received for the full 12 months of its start year unless 'Months in First Year' is set on that income item. Estimated and optimized benefits derive the claim-year months from the birth month automatically.
• Benefits indexed annually for COLA (Cost of Living Adjustment) at 2.4% (model default; user-adjustable in assumptions)
• Earnings test applied automatically: if the beneficiary claims before Full Retirement Age and has wage or self-employment income above the annual limit ($22,320 in 2024; $23,400 in 2025), benefits are withheld $1 for every $2 above the limit. In the calendar year the beneficiary reaches FRA, a higher limit applies ($59,520 in 2024; $62,160 in 2025) with $1 withheld per $3 above the limit on pre-FRA-month earnings. Withheld months are recovered via an actuarial benefit increase starting the year after FRA (5/9 of 1% per month for the first 36 withheld months, 5/12 of 1% per month thereafter).
• Full benefits not reduced by Government Pension Offset or Windfall Elimination
• Spousal and survivor benefits calculated separately when applicable
• The 35-year earnings history is SYNTHESIZED from the wage income entered in the scenario — it is not the client's actual SSA earnings record. Years before the entered wage are estimated by discounting it backward at the scenario inflation rate; years after are grown at the wage item's indexing rate. Each year is then capped at that year's Social Security wage base (SSA-published values for past years).
• AIME, PIA, and the bend points are all expressed in FRA-year dollars. SSA anchors AIME at age 60 and the bend points at the age-62 eligibility year instead. Because Stratum scales the earnings and the bend points by the same factor, and the bend-point formula is proportional, the choice of anchor year does not change the resulting benefit.

Limitations

• The earnings history is estimated, not actual. Stratum replays a full year-by-year 35-year history, but it is reconstructed from the wages entered in the scenario — not the client's real SSA earnings record. Career gaps, job changes, early low-earning years, and self-employment periods are not reflected unless they are modeled as separate wage items with explicit start and end years. Advisors holding an SSA benefit statement should enter the benefit directly as a manual social-security income item, which takes priority and skips the estimate entirely.
• Earnings are indexed at the scenario inflation rate, whereas SSA indexes at the National Average Wage Index (AWI). AWI has historically grown faster than inflation, so the estimate is deliberately conservative. The difference cancels out for most clients — the same rate is used to build the history and to index it back — but it does bite for clients earning above the Social Security wage base, whose capped years are indexed up less than SSA would. Expect estimates for high earners to run low.
• COLA assumption may differ from actual (2024 COLA was 3.2%; 2025 was 2.5%; the model default of 2.4% represents a long-run estimate)
• Earnings test uses a mid-year birthday approximation: in the calendar year FRA is reached, half the year's earned income is treated as pre-FRA. Actual pre-FRA fraction depends on birth month; advisors with clients reaching FRA mid-year should expect small (<10%) differences from SSA's actual withholding.
• Simplified spousal benefit calculation (assumes no dual entitlement)

Related

• Social Security Optimization Strategy
• Retirement Withdrawal Rate