Coast FIRE Calculator

What is Coast FIRE?

Coast FIRE is a financial milestone where your current investment portfolio is large enough to grow into your full retirement number through compound growth alone, without any additional contributions. Once you reach this point, the math works in your favor: time and market returns do the remaining heavy lifting, and you no longer need to set aside money for retirement.

The appeal of Coast FIRE lies in the optionality it creates. After crossing this threshold, your only financial obligation is covering your current living expenses. That opens the door to lower-paying but more meaningful work, reduced hours, career changes, extended travel, or simply less pressure around earning and saving. You are not yet retired — you still need income for day-to-day costs — but the retirement question is answered.

For many people, Coast FIRE represents the first concrete FIRE milestone on a longer journey. It provides a psychological shift: the knowledge that your future is funded, even if the present still requires earned income. That distinction alone can reshape how you think about work and career decisions.

How the Coast FIRE Formula Works

The calculation begins with your FIRE number — the portfolio size needed to sustain your retirement spending indefinitely. This is derived from the standard safe withdrawal rate formula:

FIRE Number = Annual Retirement Spending / Safe Withdrawal Rate

If you expect other retirement income (Social Security, pensions, annuities), only the portion of spending not covered by that income needs to come from the portfolio. The adjusted formula becomes:

FIRE Number = (Annual Spending - Other Retirement Income) / Safe Withdrawal Rate

Once you have your FIRE number, the Coast FIRE number is simply that target discounted back to today using the expected real (inflation-adjusted) rate of return and the number of years until retirement:

Coast FIRE Number = FIRE Number / (1 + Real Return)^{Years Until Retirement}

The "real return" is calculated using the Fisher equation: (1 + nominal return) / (1 + inflation rate) - 1. This is more precise than simply subtracting inflation from the nominal rate, especially over long time horizons. Using a real return ensures the result is expressed in today's purchasing power, which makes the number directly comparable to your current portfolio balance.

Here is a concrete example. Suppose you plan to spend $40,000 per year in retirement, you expect no other retirement income, and you use a 4% safe withdrawal rate. Your FIRE number is $40,000 / 0.04 = $1,000,000. If you are 30 years old, plan to retire at 65, and expect a 5% real return, your Coast FIRE number is $1,000,000 / (1.05)³⁵ = approximately $181,300. If your current portfolio exceeds that amount, you have reached Coast FIRE.

The Role of Social Security and Pensions

Guaranteed retirement income sources — Social Security, defined-benefit pensions, government pensions, or annuities — reduce the amount your investment portfolio needs to generate. If Social Security will cover $20,000 of your $40,000 annual spending, your portfolio only needs to provide the remaining $20,000. That cuts your FIRE number in half, and your Coast FIRE number drops proportionally.

This calculator includes an input for other retirement income so you can model this effect directly. For many people, especially those with substantial expected Social Security benefits or employer pensions, accounting for this income meaningfully reduces the savings target and may reveal that Coast FIRE is closer than expected.

That said, relying on future income streams introduces its own risks. Social Security benefits may be reduced by future policy changes. Pension plans can be restructured or, in rare cases, become underfunded. Annuity income depends on the issuing company's long-term solvency. It is prudent to be conservative with these estimates and to consider running the calculator both with and without other retirement income to understand the range of outcomes.

Coast FIRE vs. Other FIRE Strategies

The FIRE movement encompasses several strategies with different savings requirements, timelines, and lifestyle trade-offs. Understanding where Coast FIRE fits can help clarify which milestone you are working toward.

Full (Traditional) FIRE — Accumulate a portfolio large enough to cover all living expenses indefinitely, typically 25 times annual spending. Once you reach this number, you stop working entirely.
Coast FIRE — Save enough early that compound growth alone carries your portfolio to your FIRE number by retirement age. You still work to cover current expenses, but you no longer need to save for retirement.
Barista FIRE — Leave full-time work and take a part-time or lower-stress job. The part-time income supplements portfolio withdrawals to cover living expenses. This requires more savings than Coast FIRE but less than full FIRE.
Lean FIRE — Achieve full financial independence on a deliberately minimal budget. The portfolio target is smaller, but the lifestyle in retirement is frugal by design.
Fat FIRE — Retire with a generous spending budget that supports a comfortable or luxurious lifestyle. This requires the largest portfolio of any FIRE variant.

Coast FIRE is often the first milestone people reach on the path to other FIRE variants. It does not require you to stop working or reduce your income — it simply marks the point where continued retirement contributions become optional rather than necessary. Many people use Coast FIRE as a decision point: continue saving aggressively toward full FIRE, or shift to lower-stress work and let compounding handle the rest.

Key Assumptions and Limitations

This calculator provides a useful estimate, but like all financial projections, it relies on simplifying assumptions. Keep the following in mind when interpreting your results.

Constant real return. The calculation assumes your investments grow at a steady real rate of return each year. In practice, market returns are volatile, and the actual sequence of returns matters — particularly in the years closest to retirement.
The 4% rule has limits. The standard 4% safe withdrawal rate is based on the Trinity Study, which used historical US stock and bond returns. It may not hold for international markets, unusually long retirements, or future economic conditions that differ significantly from the past.
Taxes are not modeled. The calculator does not account for taxes on investment gains, withdrawals from tax-deferred accounts, or required minimum distributions. Your effective FIRE number may be higher once taxes are considered.
Spending is assumed constant in real terms. Annual retirement expenses are treated as flat in inflation-adjusted dollars. In reality, spending tends to vary — often higher in early retirement, lower in middle years, and higher again in late retirement due to healthcare costs.
Other retirement income is an estimate. Social Security, pension, and annuity amounts entered in the calculator are projections. Actual amounts may differ due to policy changes, early claiming penalties, cost-of-living adjustments, or other factors.

Frequently Asked Questions

What happens after I reach Coast FIRE?

Once you reach Coast FIRE, your existing portfolio is projected to grow to your retirement target through compounding alone. You still need earned income to cover your current living expenses — housing, food, insurance, and other day-to-day costs — but you can stop directing money toward retirement savings. This frees up a significant portion of your income and opens the door to career changes, reduced hours, or lower-paying work that better aligns with your interests.

Is Coast FIRE the same as being able to retire?

No. Coast FIRE means your future retirement is funded by compounding, but it does not mean you can stop working today. You still need income to pay for current expenses until you reach your target retirement age. Think of it as having the retirement question settled while the present still requires a paycheck — just not one that needs to include retirement contributions.

How accurate is the 4% withdrawal rate?

The 4% rule originates from the Trinity Study, which analyzed historical US market data and found that a 4% initial withdrawal rate (adjusted for inflation each year) sustained a portfolio for at least 30 years in the vast majority of historical periods. However, it is not a guarantee. Many financial planners recommend a more conservative rate — 3.5% or even 3% — for retirements expected to last longer than 30 years, or for those who want a wider margin of safety. The calculator lets you adjust the withdrawal rate to match your risk tolerance.

Should I really stop saving after reaching Coast FIRE?

That depends on your goals and risk tolerance. Continuing to save after reaching Coast FIRE provides a larger margin of safety against poor market returns, enables an earlier full retirement date, or funds a higher level of spending in retirement. Some people choose to redirect their savings toward other goals — paying off a mortgage, funding education, or building a cash reserve. Others simply reduce work intensity and accept a longer timeline to full FIRE. There is no single right answer; Coast FIRE gives you the flexibility to choose.