How Social Security fits into a FIRE plan

The short answer

Social Security can shrink the portfolio you need by hundreds of thousands of dollars, but it only starts between 62 and 70. The honest way to count it is in two phases: a long-term portfolio for the spending Social Security won't cover, plus a bridge for the years before your benefit begins.

For our example saver, Alex, counting a hypothetical $20,000 benefit from 67 this way lowers the FIRE number from $1,000,000 to $640,000 and moves the coast date from 7 years 7 months away to 5 months away. Allowing for a possible cut in future benefits still keeps it under two years. Either way, the coast date is a roughly 50/50 point that assumes average returns.

If you're new to these ideas, start with what FIRE is and what Coast FIRE is.

How your benefit is calculated

Social Security turns your work history into a monthly benefit in three steps:

1. Index your earnings. Each year's earnings are scaled up for wage growth since you earned them, so old pay is worth what it would be today.
2. Average your best 35 years. Your benefit is based on your highest 35 years of earnings. If you have fewer than 35, the missing years count as zeros. The total is divided by 420 months to give your average indexed monthly earnings.
3. Apply the formula. For people first eligible in 2026, your full benefit is 90% of the first $1,286 of that monthly average, 32% of the amount up to $7,749, and 15% of anything above.

The formula is deliberately progressive. It replaces a large share of low average earnings and a small share of high ones. After you start receiving it, the benefit rises each year with a cost-of-living adjustment (2.8% for 2026), so it's reasonable to plan with it in today's dollars.

What retiring early does to your benefit

Here's the catch for FIRE: every year you don't work before claiming adds nothing to your record. If you stop with fewer than 35 years, zeros fill the gap. But the progressive formula softens the blow. Take a worker whose earnings, in today's wages, average $60,000 a year in every year they work:

Working 20 years instead of 35 means 43% fewer years, but only 29% less benefit. That's good news for early retirees. It also shows why Coast FIRE is gentle on Social Security: you keep working, just without saving for retirement, so you usually build a full 35-year record anyway.

The table is a simplification. Real earnings change from year to year, and the bend points move each year with wages. Use it to see the shape of the effect, and use your own record for the numbers.

Claiming at 62, 67 or 70

Full retirement age is 67 for anyone born in 1960 or later, and 62 is the earliest you can claim. The age you choose changes your monthly benefit for life:

The reduction at 62 is 5/9 of 1% for each of the first 36 months before full retirement age and 5/12 of 1% for each month beyond. Waiting past 67 earns delayed retirement credits of 8% a year, which stop at 70. For a FIRE plan, a later claim means a bigger lifetime income but a longer gap for your portfolio to cover first. We put numbers on that trade-off below.

How to get your estimate

Sign in to my Social Security to see your earnings record and estimated benefits at different claiming ages. Check the record for missing years while you're there.

One warning matters a lot for FIRE: the estimates assume you keep earning about what you earned most recently, every year until you claim. If you plan to stop working at 45, that assumption may add 15 or more years of earnings you won't have. Two ways to adjust:

• Count your actual years of earnings by your planned stop date. If you'll have 35 or more, the estimate may be close.
• If you'll have fewer, scale it down using the table above as a rough guide. Twenty-five years of earnings instead of 35, for example, suggests a benefit roughly a fifth lower.

Two ways to fold it into your FIRE number

The quick way: subtract your expected benefit from your yearly spending and divide by your withdrawal rate. This is fine if you'll retire around the age you claim. If you retire years earlier, it overstates what Social Security does for you, because your portfolio pays everything until the checks start.

The two-phase way: split your target in two.

The long-term portfolio pays, for life, the share of spending Social Security never covers, using the 4% rule or a lower rate. The bridge covers Social Security's share until it starts.

The bridge formula ignores growth. Is that cautious? Only if you keep the bridge invested, where it will probably grow but can also drop sharply in your first years of retirement, exactly when you are spending it. That's sequence of returns risk. If you hold the bridge in cash, Treasury bills or short-term bonds to avoid that risk, assume it will roughly match inflation and no more, so the face-value amount is what you need rather than a margin.

Our calculators use one retirement age and one spending figure, so enter target × withdrawal rate as your spending. At 4%, that's target × 0.04. This is a workaround, not a perfect model: the "retire 2 years later" what-if and the odds of success don't know there's a bridge inside your spending figure, so they won't resize it. Recalculate the target for each retirement age you try.

Remember tax too. Depending on your other income, up to 85% of your Social Security benefits can be taxable, so include that tax in the retirement spending you plan for.

Alex, with and without Social Security

Alex is 32, has $185,000 invested, saves $1,500 a month and plans to retire at 60 on $40,000 a year. We assume a 7% return, no fees, 2.5% inflation and a 4% withdrawal rate. As a Coast FIRE saver, Alex keeps working until 60 and will have more than 35 years of earnings. Suppose Alex's estimate, checked against that plan, is $20,000 a year at 67 in today's dollars. This figure is hypothetical; use your own.

The two-phase target: $40,000 − $20,000 leaves $20,000 a year, which needs $500,000 at 4%. Seven years of $20,000 adds a $140,000 bridge, for $640,000. Alex enters $25,600 of spending in the calculator (4% of $640,000). The last row repeats this with only $15,600 of benefits, 78% of the estimate, for reasons explained in the next section.

The difference is large. Ignoring Social Security keeps Alex saving for 7 years 7 months. Counting it with a bridge says Alex is almost there now. The coast date still assumes average returns: across 1,000 simulated markets, the two-phase plan reaches its target by 60 in 50% of them if Alex stops saving exactly on the coast date, 62% with 3 more years of saving, and 95% if Alex never stops. That's why saving a little past the coast date is a sensible buffer.

Does the claiming age change the answer?

Using the same $20,000 estimate at 67, adjusted for claiming early or late:

On these numbers, the target barely moves: a later claim needs a bigger bridge but a smaller long-term portfolio. The bigger difference comes later in life. Claiming at 70 gives a larger inflation-adjusted income for as long as you live, which protects you if you live a long time or markets disappoint. Health, marriage and other income all matter too, so treat this as a way to compare, not a recommendation.

Social Security helps Coast FIRE more than early full FIRE

The bridge explains why. In a Coast FIRE plan you keep working until your chosen retirement age, often around 60, so the gap before claiming is short and the benefit is close to full. Someone retiring in their 40s faces a long bridge and fewer years of earnings.

Say Alex aimed for full FIRE instead. Ignoring Social Security, Alex reaches $1,000,000 in 19 years 11 months, just before 52. Counting it is circular, because an earlier retirement means both a longer bridge and fewer years of earnings. Solving for an age that works on both counts: if Alex started work at 22 and stops at 50, that's 28 years of earnings, so the benefit is about 13% lower than the full-career estimate, roughly $17,300 a year. The target becomes $567,500 for the long term plus a 17-year bridge of $294,100, or $861,600. By 50, Alex has about $889,000, enough; at 49, the target would be $881,700 against about $834,000, not enough. So Social Security lets Alex retire fully at 50 instead of just before 52, a gain of about two years.

The long bridge also matters more here: whether it's a cushion or just break-even over 17 years depends heavily on how it's invested. Still, the pattern holds: the closer you retire to your claiming age, the more Social Security does for you.

How much to count on it

Social Security has a known funding gap. The latest Trustees Report, from 2026, projects that the retirement trust fund will be depleted in late 2032. After that, incoming payroll taxes would still pay about 78% of scheduled benefits. For the retirement and disability funds combined, the projected date is 2034, with 83% payable.

That's a projection under current law, not a prediction of what Congress will do, and lawmakers have years to act. For planning, a common middle path is to count only part of your estimate, which is what the 78% row above does. For Alex, that moves the coast date from 5 months to 1 year 10 months, still far sooner than ignoring Social Security.

If you're younger or more cautious, you could count less. Whatever you pick, recheck it each year along with the rest of your plan; our guide on what to do after Coast FIRE covers the yearly check-in. If you plan to retire fully in your 40s, see also sequence of returns risk, which matters most during a long bridge.

Planning outside the US? See Coast FIRE in Canada and Coast FIRE in the UK.

Sources

Alex's results and the benefit table are our own calculations, explained on our methodology page. Rules and projections come from official sources, checked in October 2026:

1. Additional Work Can Increase Your Future Benefits. US Social Security Administration, Publication No. 05-10702. Benefits are based on your highest 35 years of earnings; years with no earnings count as zeros.
2. Social Security Benefit Amounts. US Social Security Administration, Office of the Chief Actuary. How past earnings are indexed to wage growth and averaged.
3. Primary Insurance Amount. US Social Security Administration, Office of the Chief Actuary. The 2026 benefit formula: 90%, 32% and 15% of average indexed monthly earnings, with bend points of $1,286 and $7,749.
4. Latest Cost-of-Living Adjustment. US Social Security Administration. Benefits rose 2.8% for 2026, based on the CPI-W.
5. Retirement age and benefit reduction. US Social Security Administration. Full retirement age is 67 for people born in 1960 or later; the earliest claiming age is 62.
6. Early or Late Retirement?. US Social Security Administration, Office of the Chief Actuary. Claiming at 62 with a full retirement age of 67 reduces the benefit by 30%.
7. Delayed Retirement Credits. US Social Security Administration. For people born in 1943 or later, benefits rise 8% for each year you wait past full retirement age, until 70.
8. Plan for Retirement. US Social Security Administration. How to estimate your Social Security retirement benefit.
9. Analysis of Benefit Estimates Shown in the Social Security Statement. US Social Security Administration, Office of Retirement and Disability Policy, 2020. Statement estimates assume you keep earning about what you earned most recently until you claim.
10. Publication 915, Social Security and Equivalent Railroad Retirement Benefits. Internal Revenue Service, 2025. Up to 85% of Social Security benefits can be taxable, depending on your other income.
11. The 2026 OASDI Trustees Report: Highlights. Board of Trustees, Federal OASI and DI Trust Funds, 2026. The retirement (OASI) trust fund is projected to be depleted in 2032, after which income would pay 78% of scheduled benefits; 2034 and 83% for the combined funds.
12. Determining Withdrawal Rates Using Historical Data. William P. Bengen, Journal of Financial Planning, 1994. The original 4% rule: a 4% first-year withdrawal, raised each year with inflation, lasted at least 30 years in every historical US period studied.