With Social Security, one decision moves the lifetime number more than any other — the age you start. The arithmetic behind it comes from two rules, and both go wrong when they are flattened into a single “x% a year”.
1. The early reduction is not one rate. For the first 36 months before full retirement age it is 5/9 of 1% a month (6.67pp a year); beyond that it is 5/12 of 1% (5.0pp a year). Claiming earlier is not uniformly steeper — the three years just before FRA are the expensive ones.
2. The delayed credit is one rate. For anyone born in 1943 or later it is a flat 8.0% a year, and nothing accrues after age 69.
3. The break-even age does not depend on the benefit size. Both streams scale together, so whether the amount is $700 or $4,000 a month, the crossing age is the same.
Enter your year of birth, your primary amount and the age you plan to start, and the calculator walks through the reduction or credit, the monthly benefit, and the break-even against 62, FRA and 70.
You have to supply the primary amount yourself. It comes from your lifetime earnings record, so this page cannot produce it — your own figure is in your my Social Security account at ssa.gov. Cost-of-living adjustments, taxes, the earnings test, and spousal or survivor benefits are not included. People born before 1943 have delayed-credit rates below 8.0% and are not covered here. This is an estimate.
The rule this calculator uses is SSA’s own sentence: “The percentage reduction is 5/9 of 1% per month for the first 36 months and 5/12 of 1% for each additional month.” That one sentence reproduces every row of SSA’s separately published table of reductions at 62 to two decimal places — 25.00% for 1943-1954, then 25.83%, 26.67%, 27.50%, 28.33%, 29.17%, and 30.00% for 1960 and later. We did not copy the table across; we checked that the rule produces it.
The slope bends twice
Here is someone with an FRA of 67 and a primary amount of $1,000 a month, laid out from 62 to 70 — $700 at 62, $867 at 65, $1,000 at 67 and $1,240 at 70.
That changes how the chart reads. It is not “the same cut for every year earlier”. Moving from 64 to 63 costs 5.0pp; moving from 65 to 64 costs 6.67pp. The dearest stretch is the three years immediately before FRA, and going earlier than that is actually the gentler part of the curve.
Break-even is set by the ratio, not the amount
That is the third block the calculator prints: the age at which the two cumulative streams meet. Double the benefit and the age does not move, because the early and the late stream grow by the same multiple. With an FRA of 67 the crossings are 78 years 8 months for 62 vs 67, 80 years 4 months for 62 vs 70, and 82 years 6 months for 67 vs 70 — the working is in our re-run of the 78-83 break-even.
The primary amount comes from a formula that bends twice
The primary amount is the one figure this page cannot produce — but the way it is built is published. A lifetime of earnings is indexed to average wages and averaged (that is the AIME), then cut into three slices and multiplied by 90%, 32% and 15%. For 2026 the cuts fall at $1,286 and $7,749.
Run the formula at each bend and you get $1,157 from an AIME of $1,286 and $3,226 from an AIME of $7,749. The second earner has six times the average earnings but only 2.8 times the benefit — a replacement rate of 41.6%. Earning more does raise the benefit, but on a flattening curve.
The bends move every year. They are the 1979 figures of $180 and $1,085 carried forward by average-wage growth, and SSA prints the arithmetic: $180 × 69,846.57 ÷ 9,779.44 = $1,285.59, which rounds to $1,286. That is why both numbers are re-announced annually. The AIME itself is out of reach here — it needs your earnings record.
Your year of birth settles three things at once
That is why the first field is nothing but a year. Year of birth fixes the full retirement age, the reduction at 62 and the delayed-credit rate together.
Read the columns downwards and the three behave differently. Full retirement age and the reduction at 62 move together — a later FRA means more reduction months to cover by 62 — while the delayed-credit rate changes once, at 1943, and then holds. That single step is why people born before 1943 are left out of this calculator: their rate splits into 7.0% and 7.5%.
One more rule sits underneath all of it. SSA writes: “If you were born on the 1st of the month, we figure your benefit (and your full retirement age) as if your birthday was in the previous month.” A 1st-of-the-month birthday counts as the month before, and a January 1st birthday as December of the previous year — so someone born on 1 January 1960 has a full retirement age of 66 and 10 months, not 67.
What is not in here
The primary amount itself. It is computed from your lifetime earnings record, so this page cannot invent it. Your figure is in your my Social Security account at ssa.gov.
Cost-of-living adjustments. They arrive every year, but they arrive for both the early and the late stream, so leaving them out keeps the comparison clean. That said, counted in nominal cumulative dollars they tilt towards the later claimant — the direction and the size of that tilt are measured in the article above.
Taxes, the earnings test, and spousal or survivor benefits. In particular, if you work while collecting, part of the benefit is withheld — and that money is not lost; it comes back at full retirement age, which we set out in what happens to withheld benefits.
People born before 1943. Their delayed-credit rate is below 8.0% and varies by birth year (7.5% for 1941-42, 7.0% for 1939-40, and so on). They are 84 or older in 2026, so they are left out here.
Questions that come up
What if I wait past 70?
Nothing more accrues. SSA states it plainly: “No credit is given after age 69.” The calculator stops at 70, which is exactly where the reason to keep waiting runs out.
If I file at 68, does the full 8% show up that month?
No. SSA writes: “If you retire before age 70, some of your delayed retirement credits will not be applied until the January after you start benefits.” Start before 70 and part of the credit only lands the following January. This calculator shows the amount you settle at.
Can I start on my 62nd birthday?
The calculator counts from 62 years and 0 months. Where in the month your birthday falls does move things by a month — but earlier, not later, since a 1st-of-the-month birthday counts as the month before (see the note under the table above). One month moves the reduction by 0.42 to 0.56pp.
Does this combine with the Korean national pension?
It does not. Under the US-Korea agreement, combined coverage is used for eligibility; each country still computes its own payment from its own credited periods, and the two systems start at different ages. See the full Social Security guide and the Korean national pension.
Sources and where to check
US Social Security Administration, early retirement reduction — “The percentage reduction is 5/9 of 1% per month for the first 36 months and 5/12 of 1% for each additional month.” (ssa.gov)
SSA, full retirement age and the reduction at 62 by year of birth (ssa.gov) — all seven rows reproduced from the rule above and checked against the published table. The same page carries the 1st-of-the-month rule and its January 1st corollary.
SSA, delayed retirement credits — 8.0% a year for those born in 1943 or later; “No credit is given after age 69.” (ssa.gov)
SSA, the primary insurance amount formula — the 90%, 32% and 15% slices, the 2026 bends at $1,286 and $7,749, and “$180 times 69,846.57 divided by 9,779.44 equals $1,285.59, which rounds to $1,286” (ssa.gov). The benefit at each bend — $1,157 and $3,226 — and the 41.6% replacement rate are ours, computed from that formula.
What we could not confirm — the AIME itself, the wage-indexed average of a lifetime of earnings, which comes from an individual record and sits outside this calculator.
