🔢 How to Calculate Your FIRE Number (Step-by-Step)

If you're new to the FIRE (Financial Independence, Retire Early) movement, there's one number you need to figure out before anything else: your FIRE number. It's the total amount of money you need invested before you can retire — the finish line. Once you cross it, your investments generate enough income to cover your expenses indefinitely.

This guide will walk you through calculating it step by step, explain the math behind it, and show you how to adjust it for your real situation.

What Is a FIRE Number?

Your FIRE number is the investment portfolio size at which you can stop working and live entirely off investment returns. It's calculated using the 25x Rule, which comes from the famous Trinity Study — a landmark piece of research showing that a portfolio has historically survived 30+ years of withdrawals at a 4% annual rate.

The formula is simple:

FIRE Number = Annual Expenses × 25

If you spend $50,000 per year, your FIRE number is $1,250,000. If you spend $80,000 per year, it's $2,000,000.

Step 1: Calculate Your Annual Expenses

This is the most important input — and most people get it wrong by underestimating. Be thorough.

Fixed expenses:

• Rent or mortgage
• Insurance (health, auto, home/renters)
• Loan repayments
• Subscriptions and utilities

Variable expenses:

• Food and groceries
• Transport
• Entertainment and dining out
• Travel
• Clothing and personal care

Irregular expenses (often forgotten):

• Car maintenance and replacement
• Home repairs
• Medical costs
• Gifts and holidays

Pro tip: Pull your last 12 months of bank and credit card statements rather than estimating. Most people underestimate their spending by 20–30%.

Let's say your total comes to $60,000/year.

Step 2: Apply the 25x Rule

Take your annual expenses and multiply by 25:

$60,000 × 25 = $1,500,000

That's your baseline FIRE number. A portfolio of $1.5M, invested in a diversified index fund portfolio, should — based on historical data — generate $60,000/year indefinitely using a 4% withdrawal rate.

Step 3: Understand the 4% Rule (and Its Limits)

The 4% Safe Withdrawal Rate (SWR) comes from the 1994 Trinity Study. Researchers found that a 60/40 stock/bond portfolio survived 30-year retirement windows 95%+ of the time at a 4% annual withdrawal rate.

Where it works well:

• Traditional retirement (65+) with a 25–30 year horizon
• US-based investors with historical market returns
• Flexible spending (can reduce withdrawals in down markets)

Where you should be more conservative:

• Early retirement (40s or 50s) with a 40–50 year horizon
• Non-US investors with different market dynamics
• People with inflexible, fixed expenses

For early retirees, many FIRE practitioners prefer a 3.5% withdrawal rate, which means multiplying annual expenses by ~28.5 instead of 25.

$60,000 × 28.5 = $1,710,000 (more conservative FIRE number)

Step 4: Adjust for Your Real Life

The basic formula is a starting point. Here's how to refine it:

Account for Social Security or Pension Income

If you expect $20,000/year from Social Security at 67, subtract that from your annual expenses before applying the 25x rule.

($60,000 − $20,000) × 25 = $1,000,000

This significantly reduces the portfolio you need to accumulate.

Consider Healthcare Costs

For US early retirees, healthcare before Medicare eligibility (age 65) is a major variable. Add a realistic healthcare budget to your annual expenses — this alone can add $6,000–$18,000/year depending on your situation.

Factor in Inflation

The 4% rule already accounts for inflation adjustments — you increase your withdrawal amount each year with inflation. Your FIRE number doesn't change, but your annual spending target should be in today's dollars.

Think About One-Time Large Expenses

Kids' college, a home purchase, or caring for ageing parents won't show up in your current annual expenses. Build a separate buffer or add an annual amortized amount to your expense base.

Step 5: Calculate Your Savings Rate

Now that you know your target, the next question is: how long will it take to get there?

The answer depends almost entirely on your savings rate — the percentage of your income you invest each year.

Savings Rate	Years to FIRE (approx.)
10%	~46 years
20%	~37 years
30%	~28 years
50%	~17 years
70%	~9 years

Assumes 7% real annual return, starting from zero.

This table is why FIRE enthusiasts obsess over savings rate above almost everything else. Going from a 20% to a 50% savings rate cuts nearly 20 years off your timeline.

Step 6: Track Your Progress

Your FIRE number gives you a percentage complete metric at every point:

FIRE Progress = Current Portfolio ÷ FIRE Number × 100

If you have $375,000 saved and your FIRE number is $1,500,000, you're 25% of the way there.

This is exactly what the FIRE Calculator tracks for you — your current net worth, projected growth, and the date your portfolio is expected to hit your FIRE number based on your savings and expected returns.

A Worked Example

Let's put it all together:

• Annual expenses: $65,000
• Expected Social Security at 67: $18,000/year
• Adjusted annual expenses: $65,000 − $18,000 = $47,000
• FIRE number (25x): $47,000 × 25 = $1,175,000
• Current portfolio: $220,000
• Annual savings: $30,000
• Expected return: 7% real

At those inputs, this person reaches their FIRE number in approximately 19 years.

The Bottom Line

Your FIRE number = Annual Expenses × 25. That's the starting point. From there, adjust for your withdrawal rate preference, income sources in retirement, healthcare, and any large future expenses.

The most important thing is to start with an honest picture of your spending — everything else follows from that single input.

Ready to calculate yours? Use the FIRE Calculator to enter your numbers and see exactly when you can retire.