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.
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.
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. In practice the first month of entitlement can slip depending on where in the month your birthday falls, and we could not confirm that rule in SSA’s own material. 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.
SSA, delayed retirement credits — 8.0% a year for those born in 1943 or later; “No credit is given after age 69.” (ssa.gov)
What we could not confirm — how the first month of entitlement shifts with the day of the month you were born, and the formula behind the primary amount itself. Both sit outside this calculator.
