Finance
Find your coast age.
Plan solo or household Coast FIRE with income offsets, compound growth, and currency presets.
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About this calculator
Method, formulas, and limits.What this does
Calculates the lump sum needed today so compounding alone can grow your portfolio to your retirement target. It also estimates your earliest coast age, when contributions can stop and compounding can carry you to the goal.
Who it is for
Anyone pursuing financial independence. It works for individual planners and married couples, with support for pensions, Social Security, and other fixed income offsets.
How it works
The calculator adjusts retirement spending for guaranteed income, applies your withdrawal rate to find the target portfolio, then discounts it back using real return to find the coast number. It also projects contributions year by year to find the earliest coast age.
Limitations
It assumes a constant real return and ignores sequence-of-returns risk, taxes, and market volatility. The coast number assumes zero contributions after reaching coast, which may not reflect real-world market cycles.
Key calculations
- Target portfolio
- The portfolio size needed at retirement to sustain planned spending. targetPortfolio = annualSpending / withdrawalRate
- Coast number
- The lump sum needed today so compounding to retirement equals the target portfolio. coastNumber = targetPortfolio / (1 + realReturn)^yearsToRetirement
- Real return
- Inflation-adjusted investment return derived from nominal growth and expected inflation. realReturn = (1 + nominalReturn) / (1 + inflation) − 1
- Income-adjusted spending
- Retirement spending reduced by guaranteed income that starts on or before retirement. adjustedSpend = max(0, spending − incomeAtRetirement)
Reference ranges
- Withdrawal rate
- 4% is the traditional rule for 30-year retirements. Use 3–3.5% for longer horizons or conservative planning. 5%+ may work with flexible spending or shorter timelines.
- Real return
- Historical S&P 500 real return is roughly 6–7%. Conservative planners use 4–5%. Aggressive assumptions go above 8%. Actual yearly returns vary significantly.
- Coast age
- Common coast ages range from 35 to 55 depending on savings rate, return assumptions, and spending goals. Younger coast ages require higher savings rates.
- Progress percent
- Below 50% means significant future contributions are needed. 50–80% is on track. Above 80% means the coast threshold is near or within reach.
How to use it
- 1.Choose your modeSelect Solo for individual planning or Household for joint planning with a shared portfolio and one coast age.
- 2.Enter your agesSet your current age, partner age in household mode, and target retirement age to define the compounding timeline.
- 3.Set your capitalInput current invested assets, monthly contributions, and expected annual contribution growth.
- 4.Configure market projectionsSet expected nominal return, inflation, and safe withdrawal rate for the retirement phase.
- 5.Add income streamsInclude pensions, Social Security, or other fixed income with start ages to reduce the required portfolio.
- 6.Review your resultsCheck the coast number, target portfolio, progress percentage, and earliest coast age to understand your FIRE timeline.
Coast FIRE is the point where invested assets have grown enough that, even if you stop adding new money, compounding alone can grow the portfolio to the target retirement balance by the planned retirement age. Early contributions do the heavy lifting; once you reach the coast number, you can reduce your savings rate or choose less demanding work while time and compound returns finish the job.
Yes. Switch to Household mode to plan with a shared portfolio, combined income streams, and one coast age based on the primary partner's timeline. The calculator uses the primary age as the projection clock and applies the same real return and withdrawal rate assumptions to the household balance.
Yes. Add the total value of all accounts earmarked for retirement as invested assets. The calculator does not distinguish between tax-deferred, tax-free, or taxable accounts; it treats every dollar the same. Adjust spending or withdrawal rate to approximate after-tax outcomes if needed.
Most spreadsheets use the same present-value math, but this calculator adds pension and Social Security offsets, a year-by-year contribution projection with growth, progress percentage, earliest-coast-age search, currency presets, and the gap between projected and target portfolios.
Yes. Presets are available for USD, CAD, GBP, EUR, AUD, NZD, JPY, CHF, SGD, and HKD, plus a custom option. Each preset changes the currency display and default inflation rate used in the real return calculation.
Coast age is the earliest year where the projected portfolio, including contributions up to that age, is large enough for compounding alone to reach the target by retirement. The calculator assumes contributions stop after that age, although many people continue contributing for a buffer or earlier retirement.
Income that starts on or before retirement reduces effective retirement spending, lowering the target portfolio. Income that starts later is discounted back to retirement using the real return and subtracted from the target. Guaranteed income can reduce the coast number and bring coast age earlier.
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