What Is the FIRE Number?

The FIRE number is the total investment portfolio you need to retire — or achieve financial independence — and live off your investments indefinitely. FIRE stands for Financial Independence, Retire Early.

The FIRE number is derived from the 4% rule, one of the most studied concepts in retirement planning.

The formula

FIRE Number = Annual Expenses in Retirement × 25

Why 25? Because 25 is the inverse of 4% (1 / 0.04 = 25). If you withdraw 4% of your portfolio per year, you need 25× your annual expenses to sustain withdrawals indefinitely.

Example: If you plan to spend $50,000 per year in retirement:

FIRE Number = $50,000 × 25 = $1,250,000

You need $1.25 million invested to retire (under the 4% rule).

Where does the 4% rule come from?

The 4% rule comes from the Trinity Study (1998), which examined historical US stock and bond returns from 1926 to 1995. The researchers found that a portfolio split 60% stocks / 40% bonds could sustain a 4% withdrawal rate for 30 years with a very high probability of success.

Key caveats:

• The study used historical US market returns, which were above average.
• It modelled a 30-year retirement — not a 40 or 50-year one.
• It did not account for sequence-of-returns risk in extreme market crashes.

Is 4% still safe for early retirees?

Many FIRE practitioners argue that a 4% withdrawal rate is too aggressive for someone retiring at 40 with a 50+ year time horizon. Common adjustments:

Withdrawal rate	Multiplier	Suitable for
4%	25×	Standard 30-year retirement
3.5%	~29×	Early retirees (40–50 year horizon)
3%	~33×	Very early retirees, conservative
2.5%	40×	Extremely cautious / large buffer

The "right" rate depends on your:

• Retirement age and expected horizon
• Portfolio allocation (stocks vs bonds vs real estate)
• Flexibility to reduce spending in down markets
• Other income sources (part-time work, Social Security, pension)

How to estimate years to FIRE

A simple (conservative) estimate ignores investment growth:

Years to FIRE ≈ Savings Gap ÷ Annual Savings

Where Savings Gap = FIRE Number − Current Portfolio.

This is conservative because it ignores investment returns on your existing and new contributions. A realistic estimate should compound both your current portfolio and future contributions at an expected real return (e.g. 5–7% after inflation).

Example with 0% growth:

• FIRE Number: $1,250,000
• Current portfolio: $100,000
• Savings Gap: $1,150,000
• Annual savings: $24,000
• Simple years to FIRE: 1,150,000 / 24,000 ≈ 48 years

With 7% real return, the same scenario takes closer to 22 years — significantly different. Use the Retirement Calculator for compound-growth projections.

FIRE variants

The FIRE community has developed several variants to suit different lifestyles:

Variant	Description
Lean FIRE	Very frugal lifestyle, FIRE number typically $500k–$1M
Standard FIRE	Comfortable middle-class lifestyle
Fat FIRE	Wealthy lifestyle, FIRE number $2.5M+
Barista FIRE	Semi-retire, cover healthcare/expenses with part-time work
Coast FIRE	Stop contributing now — existing portfolio will compound to FIRE number by traditional retirement age

What to include in annual expenses

Be realistic and include:

• Housing (rent or equivalent carrying cost for owned home)
• Food and groceries
• Healthcare — especially if pre-Medicare in the US
• Transport
• Travel and leisure
• Insurance premiums
• Clothing, personal care
• A buffer for irregular large expenses (car replacement, home repairs)

Most people underestimate healthcare costs before age 65 in the US. Individual health insurance premiums can easily exceed $6,000–$12,000 per year.

After you hit the FIRE number

Reaching your FIRE number does not mean you must stop working. It means you have the option to. Many FIRE retirees continue to generate income through passion projects, consulting, or part-time work — which reduces withdrawal pressure and extends portfolio longevity.