FIRE Number Calculator Summary
Core Concept: The 4% Rule
This calculator is based on the 4% rule, which comes from the Trinity Study. The rule suggests that if you withdraw 4% of your investment portfolio in the first year of retirement and then adjust that dollar amount for inflation each year, you have a high probability of your money lasting at least 30 years (based on historical U.S. stock and bond returns).
Because 4% is 1/25, your FIRE number (the amount you need invested to retire) is:
FIRE Number = Annual Expenses Ă— 25
So:
- If you spend $50,000/year, your FIRE number is $1,250,000.
- If you spend $80,000/year, your FIRE number is $2,000,000.
Every $1,000 reduction in annual spending lowers your FIRE number by $25,000, which can significantly shorten your time to financial independence.
What Is a FIRE Number?
Your FIRE number is the total amount of invested assets you need so that you can cover your living expenses without working. It’s the target portfolio size at which you can, in principle, live off your investments indefinitely using a sustainable withdrawal rate.
Formula:
- FIRE Number = Annual Expenses Ă— 25
- Annual expenses should include everything: housing, food, transportation, insurance, healthcare, entertainment, travel, and all other recurring costs.
The logic:
- 25 × expenses → portfolio size.
- 4% of that portfolio → exactly 1 year of expenses.
How This Calculator Works
- You enter:
- Annual expenses (total yearly spending)
- Current savings (invested assets you already have)
- Monthly contribution (how much you’re adding to investments each month)
- The calculator computes:
- Your FIRE number using:
annual expenses Ă— 25 - How far along you are: current savings Ă· FIRE number
- An estimated timeline (in years) to reach your FIRE number, based on:
- Your starting savings
- Your ongoing monthly contributions
- You can run scenarios:
- Lower annual expenses to see how much your FIRE number drops.
- Increase monthly contributions to see how your timeline shortens.
- Combine both to see the compounding effect on your path to FI.
How to Use the Calculator Effectively
- Enter realistic annual expenses.
Be comprehensive and honest. Underestimating expenses is one of the most common FIRE mistakes.
- Input current savings.
Include only invested assets earmarked for retirement/FI (e.g., brokerage accounts, retirement accounts, etc.).
- Add your monthly contribution.
This is how much you’re consistently investing each month toward FI.
- Review the outputs:
- Your FIRE number (target portfolio size)
- Your progress percentage toward that number
- The estimated years until you reach FI
- Experiment with changes:
- Reduce expenses (e.g., by $5,000–$10,000/year) and see how much earlier you could reach FI.
- Increase your savings rate (higher monthly contributions) and compare timelines.
Important Caveats and Considerations
- Not a guarantee:
The 4% rule is based on historical U.S. market data; future returns may differ.
- Retiring very early:
The original research modeled 30-year retirements. If you’re planning for 40–50+ years, many planners recommend a more conservative withdrawal rate, such as 3.5%.
- Healthcare costs:
Especially critical if you retire before age 65 (before Medicare eligibility in the U.S.). Healthcare can be a major and volatile expense.
- Changing expenses:
Your spending in retirement may not match your current spending:
- Some costs may decrease (commuting, work clothes, certain work-related expenses).
- Others may increase (healthcare, travel, hobbies, family support).
- Ongoing adjustments:
Use this calculator as a directional guide, not a one-time verdict. Revisit your numbers regularly as your income, lifestyle, goals, and market conditions change.
In summary, this FIRE calculator:
- Uses the 4% rule to convert your annual expenses into a target portfolio (your FIRE number).
- Incorporates your current savings and monthly contributions to estimate how long it may take to reach FI.
- Helps you see how changes in spending and saving can dramatically alter your FI timeline.