Coast FIRE with a pension & Social Security

Retirement income gaps in today’s dollars

Withdrawals occur at the start of each year, then the remaining portfolio earns the real return. Excess benefit income is not reinvested.

A coast target that includes benefit start dates

Coast FIRE means existing investments are projected to grow to a retirement target without further retirement contributions. It still assumes you fund your living expenses before retirement from another source. This version models the spending gap year by year instead of applying a withdrawal percentage to one income figure.

All inputs and outputs use today’s purchasing power. Enter real investment returns after inflation and fees. Enter a benefit amount expressed in today’s dollars at its selected start age. If a statement quotes future inflated dollars, convert that amount to today’s dollars first. Check whether an estimate assumes continued employment; stopping work earlier may change a benefit estimate.

For each retirement year, the portfolio gap is max(0, spending budget − pension − Social Security). A benefit does not reduce the gap until its start age. The spending budget should include the taxes and other expenses you need to fund, so that subtracting gross benefits is consistent with the budget.

How the required balance is calculated

For retirement age R and end age E, let gap(a) be the year’s spending gap and r be the real retirement return. Required assets at retirement equal Σ gap(a) / (1 + r)^{a − R} for ages R through E − 1. The first withdrawal occurs immediately at retirement. The final required balance at age E is zero.

The coast amount today is that retirement target divided by (1 + real pre-retirement return)^{years until retirement}. Returns before and during retirement can differ. The result is a deterministic present-value calculation for the selected horizon; it is not a safe-withdrawal-rate study or a probability of avoiding depletion.

The comparison with no benefits removes both the pension and Social Security while retaining the same spending, ages and return assumptions. The projected-assets line uses your current savings, with no further contributions, and reports the first retirement year in which the full modeled gap cannot be paid.

Example: retire at 60, benefits begin at 67

Suppose annual spending is $60,000, the pension is zero, Social Security is $2,000 a month starting at 67, and spending is funded until age 90. At a 0% real retirement return, seven years from ages 60 through 66 require $420,000. The next 23 years require $36,000 per year after benefits, or $828,000.

Total assets needed at 60 are therefore $1,248,000. For someone age 40 assuming 5% real growth before retirement, the coast amount today is $1,248,000 ÷ 1.05²⁰, approximately $470,358. Subtracting benefits from spending starting at age 60 would omit the seven-year bridge and understate the target.

A fixed pension can lose purchasing power

Choose whether your pension keeps pace with inflation after it begins. In the fixed-payment option, its value in today’s dollars falls each year by the assumed inflation factor. The pension input is its purchasing power at the start age, expressed in today’s dollars; before that age the model pays nothing.

For example, a pension worth $1,000 monthly at its start loses purchasing power to about $554 after 20 years of 3% inflation if its nominal payment never rises. The Social Security input is assumed to maintain its purchasing power after claiming. Actual future adjustments may not match your household’s expenses.

This model omits survivor elections, partial pension adjustments, benefit reductions, account-access penalties and market volatility. It does not fund living past the selected end age or leave a required inheritance. Test later end ages, lower returns and reduced benefits; use the early retirement bridge tool to inspect account access during the gap years.

Frequently asked questions

Is this the same formula as the standard Coast FIRE calculator?

No. This version discounts annual spending gaps over a finite horizon and targets zero required assets at the end. The standard tool uses a withdrawal-rate target. Different assumptions can produce different coast numbers.

Does a pension reduce the bridge years before it starts?

No. Pension income is zero before the pension start age. Social Security is also excluded until its selected start age.

Can I stop working when the current balance exceeds the coast target?

The calculation alone does not establish that. It assumes living expenses before retirement are funded elsewhere and uses fixed returns, a selected end age and the benefits you entered. It does not test market uncertainty or account-access constraints.

Sources & model notes

• Social Security Administration: benefit estimates and earnings assumptions
• Social Security Administration: plan for retirement

Calculator, formulas and examples by FinancialDepth, checked October 23, 2026. Sources explain the underlying account or product rules; numerical projections come from the assumptions shown on this page. See our methodology and limitations.

Continue planning

• Use the standard Coast FIRE model
• Plan access during the bridge years
• Explore savings longevity

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