Coast FIRE Calculator with Social Security
Your coast number already includes decades of Social Security you paid for. Most calculators pretend it does not exist.
Enter your benefit estimate from ssa.gov, pick a claiming age, and the calculator splits the target: full spending until benefits start, then only the gap your portfolio still covers.
Your Results
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Coast FIRE with Social Security: the claiming age is the lever
For the 1960-and-later cohort, full retirement age is 67. Claim at 62 and the check shrinks to 70% of your full benefit for life; wait until 70 and it grows to 124%. Those factors come straight from the Social Security Administration's reduction and credit tables, and this calculator applies them to the estimate you enter.
Claiming age moves two parts of the coast math in opposite directions. Later claiming means a bigger benefit and a smaller perpetual gap for your portfolio, but more bridge years to fund before the checks start. Bridge years cost one dollar per dollar of missing benefit, while the perpetual gap costs 25 dollars per dollar at a 4% withdrawal rate. That asymmetry is why waiting usually shrinks the total, and the comparison line under the results shows all three ages so you never have to take it on faith.
The two-phase structure is the same as the pension version: full spending until income starts, only the gap afterward. What is different here is that the income itself depends on a decision you control.
Claiming age compared, with this page's defaults
Retire at 62, $24,000 full-retirement-age benefit, $50,000 spending, 4% withdrawal rate, 7% return, coast number at age 35. The same run the calculator shows live, baked as a table.
| Claim at | Benefit per year | Portfolio needed at 62 | Coast number at 35 |
|---|---|---|---|
| 62 | $16,800 | $830,000 | $133,572 |
| 67 | $24,000 | $770,000 | $123,916 |
| 70 | $29,760 | $744,080 | $119,745 |
What this calculator assumes (and what it leaves out)
The benefit is applied exactly as the SSA factors promise, for life, with no trust-fund haircut unless you build one into the estimate yourself (the FAQ shows how). Spousal and survivor benefits, taxes on benefits, and the earnings test for working while claiming are not modeled. Social Security is inflation-adjusted, so pairing this tool with a real return of about 5% keeps every number in today's dollars.
Sources: SSA reduction and delayed-credit tables at ssa.gov, William Bengen's 1994 study, and the 1998 Trinity Study. Last reviewed: July 25, 2026, formulas verified against the site's shared coast math.
Frequently asked questions
Where do I find my Social Security benefit estimate?
Log in at ssa.gov and open your Social Security Statement. It shows your estimated monthly benefit at 62, at full retirement age, and at 70. Enter the full-retirement-age figure here as an annual amount (monthly times 12); the claiming-age buttons apply the official reduction and credit factors for you.
Why does claiming later lower my coast number?
Two effects pull the same direction. Claiming at 70 pays 24% more than at 67 for the 1960-and-later cohort, so the perpetual gap your portfolio covers gets smaller. The bridge before benefits start gets longer, but bridge years are funded dollar for dollar while the perpetual part is funded at 25 times the gap, so shrinking the gap usually wins. The comparison line under the results shows all three claiming ages so you can see it directly.
Will Social Security even exist when I retire?
The honest answer: the trust fund projections point to a shortfall in the 2030s that would cut benefits to roughly 75 to 80 percent of the promised amount if Congress does nothing, not to zero. A reasonable conservative run is to enter 75 to 80 percent of your statement's estimate and see how the coast number holds up. Planning for zero is a choice, not a forecast.
Is the benefit inflation-adjusted?
Yes, Social Security has an annual cost-of-living adjustment, which makes it a natural fit for running this calculator with a real return of about 5%: then the benefit, your spending, and the growth all read in today's dollars. That combination is the cleanest honest setup this tool offers.
What about spousal or survivor benefits?
Not modeled. Spousal and survivor rules are a genuinely different calculation with their own claiming interactions. If your household expects two benefits, a rough conservative approach is to run the couples calculator with the smaller benefit folded into reduced household spending, and treat the result as a floor.
Who runs this site?
Jonas, on my own. This variant exists because claiming age is the one retirement decision almost everyone gets to make, and no free coast calculator I could find showed what it does to the number. Free, no login, and your inputs never leave the browser. A $27 ebook and a $67 workbook pay for the site. Not a financial advisor; the about page has the rest.
Have a pension instead?
The pension version runs the same two-phase math with a fixed amount and start age.
Open the pension version →