FIRE Number Calculator

What is a FIRE Number?

Your FIRE number is the investment portfolio size needed to sustain your retirement spending indefinitely. It is the central target of the Financial Independence, Retire Early movement — the point at which your wealth generates enough income to replace your paycheck for good.

The formula is straightforward: divide your annual spending by your safe withdrawal rate. If you spend $40,000 per year and use a 4% withdrawal rate, your FIRE number is $1,000,000. That portfolio, drawn down at a sustainable pace, is projected to last through a full retirement.

If you expect other retirement income — Social Security, a pension, or annuity payments — only the gap between your spending and that income needs to come from the portfolio. This can substantially reduce the amount you need to save, making financial independence more attainable than the raw spending figure might suggest.

How the FIRE Number Formula Works

The core calculation is a single division. Start with your annual retirement spending, subtract any guaranteed retirement income, and divide by your safe withdrawal rate:

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

Here is a concrete example. Suppose you expect to spend $50,000 per year in retirement and anticipate $10,000 annually from Social Security. Using a 4% safe withdrawal rate, your FIRE number is ($50,000 - $10,000) / 0.04 = $1,000,000. Your portfolio needs to cover the $40,000 gap, and at a 4% withdrawal rate, $1,000,000 is the balance required to do that sustainably.

The safe withdrawal rate — commonly set at 4% — originates from the Trinity Study, which analyzed decades of US market data and found that withdrawing 4% of an initial portfolio balance (adjusted for inflation each year) sustained the portfolio for at least 30 years in the vast majority of historical periods. This 4% figure translates to the well-known "25x rule": you need roughly 25 times your annual withdrawal amount saved.

All numbers in this calculator are expressed in today's dollars — real, inflation-adjusted terms. This means your FIRE number represents purchasing power you can relate to right now, not a nominal figure that will look different decades from now.

How Long Until You Reach Your FIRE Number?

Beyond calculating the target itself, this tool projects how long it will take to get there given your current savings, annual contributions, and expected investment returns. The projection works by growing your portfolio forward year by year with compound growth plus regular contributions until it reaches the FIRE number.

To keep everything in today's purchasing power, the calculator converts your nominal expected return into a real return using the Fisher equation: (1 + nominal return) / (1 + inflation rate) - 1. This is more precise than simply subtracting inflation from the nominal rate, particularly over long time horizons. Working in real terms means the projected timeline and portfolio values are directly comparable to your current financial situation without needing to guess at future price levels.

The Role of Safe Withdrawal Rate

The safe withdrawal rate is the single most influential variable in the FIRE number formula. A small change in the rate produces a large change in the target portfolio. At 4%, you need 25 times your annual withdrawals. At 3.5%, that rises to roughly 28.6 times. At 3%, it climbs to 33.3 times.

The widely cited 4% rule is grounded in the Trinity Study, which examined rolling 30-year periods of US stock and bond returns. For a traditional retirement starting around age 65, 4% has strong historical support. However, early retirees face a longer time horizon — someone retiring at 40 may need their portfolio to last 50 or 60 years. Many financial planners recommend a more conservative rate of 3% to 3.5% for these longer retirements to provide a wider margin of safety against poor market sequences.

A higher withdrawal rate produces a smaller, more reachable FIRE number, but it increases the risk that the portfolio will not last. A lower rate demands more saving but provides greater resilience. The calculator lets you adjust this rate so you can see how different assumptions affect your target and timeline.

Reducing Your FIRE Number

The most direct way to lower your FIRE number is to reduce your annual spending. Every dollar removed from your retirement budget reduces the target by $25 at a 4% withdrawal rate. This is why spending control is the most powerful lever in early retirement planning — it simultaneously lowers the goal and frees up more money to save toward it.

Guaranteed retirement income also reduces your FIRE number. Social Security, a defined-benefit pension, or annuity income offsets the amount your portfolio needs to provide. If Social Security will cover $15,000 of your $50,000 annual spending, your portfolio only needs to generate $35,000, which lowers the target from $1,250,000 to $875,000 at a 4% rate.

Choosing a higher safe withdrawal rate also reduces the target, though this comes with increased risk of portfolio depletion over a long retirement. Some people accept this trade-off by planning for part-time work in early retirement — an approach known as Barista FIRE — which supplements portfolio withdrawals and reduces the balance needed at the start.

FIRE Number vs. Other FIRE Milestones

The FIRE number is the full financial independence target, but the FIRE movement includes several intermediate and alternative milestones that reflect different balances of savings, work, and lifestyle.

Full FIRE — The FIRE number itself. Your portfolio covers all living expenses indefinitely, and you no longer need earned income of any kind.
Coast FIRE — You have saved enough that compound growth alone will carry your portfolio to your FIRE number by retirement age. You still work to cover current expenses, but retirement contributions are no longer necessary.
Barista FIRE — You 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.

These milestones are not mutually exclusive. Many people pass through Coast FIRE on the way to full FIRE, or plan for Barista FIRE as a transitional phase. The FIRE number serves as the reference point around which the other strategies are defined — each one is essentially a different relationship to that central target.

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 projection 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 just before and after 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 is a good FIRE number?

There is no universal answer — your FIRE number is determined entirely by your spending. The standard reference point is 25 times your annual spending at a 4% safe withdrawal rate. Someone spending $40,000 per year needs $1,000,000. At $80,000 per year, the target doubles to $2,000,000. The "right" number is the one that covers your specific lifestyle at a withdrawal rate you are comfortable with.

Does the FIRE number include Social Security?

If you expect reliable retirement income from Social Security, a pension, or another source, it reduces the amount your portfolio needs to provide. Rather than covering all of your spending from investments, you only need to cover the gap. The calculator's "Other Retirement Income" field lets you account for this directly, which can meaningfully lower your FIRE number.

Should I use 4% or something lower?

The 4% rule was designed around 30-year retirements — a reasonable assumption for someone retiring at 65. If you plan to retire significantly earlier, say at 40 or 45, your portfolio may need to last 50 years or more. In that case, a withdrawal rate of 3% to 3.5% provides a larger safety margin against poor market conditions and reduces the chance of running out of money late in life. The trade-off is a higher FIRE number and a longer accumulation phase.

What if I want to retire early but still work part-time?

That approach is commonly known as Barista FIRE. Instead of building a portfolio large enough to cover all expenses, you supplement withdrawals with part-time income. This allows you to leave full-time work earlier with a smaller portfolio. The Barista FIRE calculator can help you model how much part-time income you would need and how it affects your savings target.