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Financial Independence Number Calculator

Reviewed by the CalculatorHub team, edited by James Graham. Trinity Study 4% rule. Last verified 14 June 2026.

Your financial independence number is the total investment portfolio you need to retire and live off investment returns indefinitely without running out of money. The most widely accepted framework comes from research published by Cooley, Hubbard, and Walz (1998), which found that a 4% annual withdrawal rate from a diversified portfolio succeeded over 30-year retirement periods across most historical scenarios. This translates to the "25x rule": multiply your desired annual spending by 25 to get your FI number. Reaching this number means you can, in theory, retire and sustain your lifestyle through investment returns alone. This calculator computes your FI number at multiple withdrawal rates and shows your current savings gap.

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Financial independence number formula

Portfolio-Funded Expenses = Annual Expenses - Annual Guaranteed Income
FI Number = Portfolio-Funded Expenses / (Withdrawal Rate / 100)
Equivalently: FI Number = Portfolio-Funded Expenses x (100 / Withdrawal Rate)
Savings Gap = max(0, FI Number - Current Portfolio)

At a 4% withdrawal rate, the multiplier is 25x. At 3.5% it is 28.6x. At 3.25% it is 30.8x.

Common FIRE withdrawal rate targets

  • 4% (25x): classic Trinity Study threshold; suitable for 30-year retirements.
  • 3.5% (28.6x): conservative choice; suitable for 40-50 year early retirements.
  • 3.25% (30.8x): very conservative; often used by early retirees with no fallback income.
  • 4.5-5% (20-22x): sometimes used when there is significant guaranteed income or flexibility to cut spending.

Financial independence number: frequently asked questions

What is the financial independence number?

Your financial independence number (also called your FIRE number) is the total investment portfolio value you need to sustainably withdraw your desired annual spending for the rest of your life without depleting the portfolio. The most widely cited calculation uses the 4% safe withdrawal rate: FI Number = Annual Expenses / 0.04, or equivalently, Annual Expenses x 25.

What is the 4% safe withdrawal rate?

The 4% safe withdrawal rate emerged from the Trinity Study (Cooley, Hubbard, Walz, 1998) and its subsequent updates. Research showed that a diversified portfolio of stocks and bonds historically sustained a 4% annual withdrawal rate for 30 years with a high success rate. The 4% rate has held up across most historical periods, including the Great Depression. Some researchers use 3.5% for longer retirement periods (40+ years).

Should I use 4% or a different withdrawal rate?

The 4% rule was designed for 30-year retirements. If you retire early (at 40 or 45), your retirement could last 50+ years, in which case many FIRE community members use 3.5% (your number x 28.6) or 3.25% (x 30.8) for extra safety margin. If you have other income sources (part-time work, Social Security, rental income), you can use a higher rate because you do not need to withdraw as much from investments.

Do I need to include Social Security in my FI number?

You can reduce your FI number by the present value of expected Social Security benefits, or more simply, reduce your annual spending target by your expected monthly Social Security benefit. For example, if your expenses are $60,000 per year and Social Security will cover $18,000 per year, you only need your portfolio to cover $42,000, giving a FI number of $1,050,000 (at 4%) rather than $1,500,000.

How long will it take me to reach my FI number?

The number of years to reach FI depends on your current portfolio, savings rate, and investment return. This calculator shows the FI number and your current savings gap. For time-to-FI projections, use the wealth accumulation calculator, which models portfolio growth to your target. In general, a 25-30% savings rate can achieve FI in 25-30 years; a 50%+ savings rate can achieve FI in 15-17 years.

Official sources and references

Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.