How to Calculate Your FIRE Number

Your FIRE number is the total investment portfolio you need to retire and live off your investments indefinitely. It's the single most important figure in all of FIRE planning — the target you're working toward, the number that tells you exactly how far you are from financial independence.

Calculating it is simple. Understanding the math behind it — and the assumptions baked into it — is what separates people who plan confidently from those who worry they've gotten it wrong.

The Formula

FIRE Number = Annual Expenses ÷ Safe Withdrawal Rate

At the most widely used safe withdrawal rate of 4%:

FIRE Number = Annual Expenses × 25

That's it. If you spend $50,000 per year, your FIRE number is $1,250,000. If you spend $60,000, it's $1,500,000. Every dollar you cut from annual spending reduces your FIRE number by $25.

Use the FIRE Number Calculator to calculate yours instantly.

What Is the Safe Withdrawal Rate?

The safe withdrawal rate (SWR) is the percentage of your portfolio you can withdraw each year without running out of money over a long retirement.

The 4% figure comes from William Bengen's 1994 research and was later confirmed by the Trinity Study (1998), conducted by three Trinity University professors. They analyzed historical market data from 1925 to 1995 and found that a portfolio invested 50–75% in stocks and the rest in bonds survived a 4% annual withdrawal rate for 30 years in virtually every historical scenario — including the Great Depression and the stagflation of the 1970s.

The practical implication: if your portfolio equals 25× your annual expenses, history suggests you can withdraw 4% per year (adjusted for inflation) and never run out of money.

Step-by-Step: Calculating Your FIRE Number

Step 1: Determine your annual expenses

This is your actual spending — everything you spend in a year. Not income, not savings. Spending.

Track at minimum 3 months of expenses. Include:

• Housing (rent/mortgage, utilities, insurance, maintenance)
• Food (groceries + restaurants)
• Transportation (car payment, insurance, gas, public transit)
• Healthcare (insurance premiums, out-of-pocket costs)
• Subscriptions and recurring services
• Travel and entertainment
• Clothing, household goods
• Gifts, charitable giving
• Any irregular but expected expenses (car replacement, home repairs)

Be honest. Underestimating expenses is the most common FIRE planning mistake. Build in a 10–15% buffer for expenses you haven't thought of.

Step 2: Project future expenses

Your current expenses and your retirement expenses may differ. Consider:

• Will your mortgage be paid off?
• Will you have children to support?
• Will healthcare costs increase (likely, if retiring before Medicare eligibility at 65)?
• Will you travel more or less?
• Do you plan to relocate to a lower or higher cost area?

For most people, early retirement expenses are similar to or slightly higher than working-years expenses. Travel, hobbies, and healthcare tend to fill the gap left by commuting and work-related costs.

Step 3: Choose your withdrawal rate

4% is the standard starting point, appropriate for 30-year retirements.

3.5% (FIRE Number = annual expenses × 28.6) is more conservative and better suited for 40-year retirements — meaning retiring at 55 and living to 95.

3% (FIRE Number = annual expenses × 33.3) is the most conservative widely used rate, appropriate for 50+ year retirements — retiring at 40 with a 55-year horizon.

Lower withdrawal rates require a larger portfolio but provide more margin for bad market timing, healthcare surprises, and lifestyle changes.

Step 4: Do the math

Annual Expenses × (1 ÷ Withdrawal Rate) = FIRE Number

Or simply multiply by the corresponding factor:

| Withdrawal Rate | Multiply Expenses By | |---|---| | 4.0% | 25× | | 3.5% | 28.6× | | 3.25% | 30.8× | | 3.0% | 33.3× |

Examples

Example 1: Standard Early Retiree

• Annual expenses: $48,000
• Withdrawal rate: 4%
• FIRE Number: $1,200,000

At a 50% savings rate and 7% real returns, this person reaches their FIRE number in approximately 17 years.

Example 2: Conservative Long Retirement

• Annual expenses: $55,000
• Plans to retire at 40 (55-year horizon)
• Withdrawal rate: 3.25% (×30.8)
• FIRE Number: $1,694,000

The extra buffer adds $494,000 to the target but significantly reduces the risk of portfolio failure late in retirement.

Example 3: Lean FIRE

• Annual expenses: $30,000 (frugal lifestyle, low cost-of-living area)
• Withdrawal rate: 4%
• FIRE Number: $750,000

The dramatically lower target makes this achievable in as few as 10–12 years for a high-saver. A $750,000 portfolio is well within reach for many middle-class earners.

Example 4: Fat FIRE

• Annual expenses: $120,000 (comfortable lifestyle, two kids, regular travel)
• Withdrawal rate: 3.5% (conservative, planning to retire at 50)
• FIRE Number: $3,428,571

Fat FIRE requires a significantly larger portfolio, typically requiring a high-income career and sustained high savings rate. But many dual-income professional households can reach this number.

What Counts Toward Your FIRE Number?

Only liquid, invested assets count:

Counts:

• 401(k), 403(b) balances
• Traditional and Roth IRA balances
• Taxable brokerage accounts
• HSA balances (after 65, or for medical expenses at any age)

Does not count:

• Primary residence equity (it doesn't generate income unless you sell or rent)
• Illiquid assets (collectibles, private business equity unless you're monetizing it)
• Emergency fund cash (this is separate from your investment portfolio)

May count, with caveats:

• Rental property equity (if the net rental income factors into your expense calculation, the property value can be excluded)
• Social Security and pension income (reduces your required withdrawal amount, effectively lowering your needed portfolio)

Social Security and Pensions: How They Change the Math

If you'll receive Social Security or pension income in retirement, you don't need your portfolio to cover 100% of your expenses. You only need to cover the gap.

Example:

• Annual expenses: $60,000
• Expected Social Security at 67: $18,000/year
• Gap to cover from portfolio: $42,000
• FIRE Number at 4%: $42,000 × 25 = $1,050,000

vs. without Social Security: $60,000 × 25 = $1,500,000

Social Security reduces this person's required portfolio by $450,000 — a significant difference. For people retiring early (before 62), Social Security won't be available for decades, so it generally shouldn't be relied upon heavily in the early years.

The Sequence-of-Returns Risk

One important caveat to the 4% rule: it assumes average returns. What hurts early retirees is poor returns in the first few years of retirement — known as sequence-of-returns risk.

If the market drops 30% in year one of your retirement and you're still withdrawing 4%, you sell more shares at depressed prices. Those shares never recover the same amount of growth. This can accelerate portfolio depletion even if long-run returns are fine.

Common mitigations:

• Use a more conservative withdrawal rate (3–3.5%)
• Hold 1–3 years of expenses in cash or short-term bonds
• Reduce discretionary spending in bad market years
• Maintain a small income source (consulting, part-time work) in early retirement

Tracking Progress

Once you know your FIRE number, track your progress as a percentage:

FIRE Progress = Current Portfolio ÷ FIRE Number × 100

At 25% of your FIRE number, you've covered one year of expenses per four years needed. At 50%, you're halfway. When you hit 100%, you've reached financial independence.

The FIRE Calculator shows this progress visually, including a year-by-year portfolio projection to your FIRE date.

Related Tools and Articles

• FIRE Calculator — Full retirement timeline with year-by-year projections
• Investment Growth Calculator — Project your portfolio growth over time
• Savings Rate Calculator — See how your savings rate affects your timeline
• Coast FIRE Calculator — Find out if you can stop contributing now
• How Investment Growth Works — The math behind compound returns
• What Is FIRE? — The full beginner's guide to financial independence
• The 4% Rule Explained — Deep dive into safe withdrawal rate research

This article is for educational purposes only. It does not constitute financial, tax, or investment advice. Consult a qualified financial professional for personalized guidance.