Retirement & FIRE Calculator

How to Use This Calculator

1. Enter your ages — your current age and when you want to retire. Try different retirement ages to see the impact on your savings.
2. Add your savings — current retirement savings (all accounts combined) and how much you contribute each month.
3. Set return and inflation — expected investment return (7% is a common balanced estimate) and inflation rate (2.5% US average).
4. Plan your spending — estimate monthly expenses in retirement and any Social Security income you expect.
5. Read the results — the calculator shows your FIRE number, projected balance, monthly retirement income, and how long your money lasts.

Understanding Retirement & FIRE Planning

Retirement planning boils down to one question: will your savings last as long as you do? The answer depends on how much you save, how your investments grow, how much you spend, and how long your retirement lasts.

The FIRE movement (Financial Independence, Retire Early) popularized a simple formula: save 25x your annual expenses, then withdraw 4% per year. If your expenses are $48,000/year, your FIRE number is $1,200,000. This approach, based on the 4% rule from the Trinity Study, has a high probability of lasting 30+ years.

Social Security reduces the amount you need to save. If you expect $1,500/month from Social Security, your savings only need to cover the gap between your expenses and your benefit. This can reduce your FIRE number by hundreds of thousands of dollars.

The most powerful variable is time. Starting to save at 25 vs 35 can double your retirement balance, thanks to compound growth. If you're starting late, increasing your savings rate is the most effective lever — going from 10% to 20% of income can make up for a decade of lost compounding.

Frequently Asked Questions

What is the FIRE number?

Your FIRE (Financial Independence, Retire Early) number is the amount of savings you need so that annual withdrawals cover your expenses indefinitely. It's calculated as your annual expenses divided by your withdrawal rate. With $4,000/month in expenses, $1,500 in Social Security, and a 4% withdrawal rate, your FIRE number is ($2,500 × 12) / 0.04 = $750,000.

What is the 4% rule?

The 4% rule is a guideline from the Trinity Study suggesting you can withdraw 4% of your portfolio in year one of retirement, then adjust for inflation each year, and your money should last at least 30 years. It assumes a balanced stock/bond portfolio. For early retirees (40+ year retirements), many financial planners recommend a more conservative 3-3.5% withdrawal rate.

How does inflation affect retirement planning?

Inflation is one of the biggest threats to a retirement plan. At 2.5% inflation, $4,000 in today's expenses will cost about $6,700 in 20 years and $11,200 in 40 years. This calculator adjusts expenses for inflation during retirement and shows both nominal and inflation-adjusted portfolio values, so you can see the real purchasing power of your savings.

Should I include Social Security in my plan?

Yes, but conservatively. Social Security currently replaces about 40% of pre-retirement income for average earners. Check your projected benefit at ssa.gov. For FIRE planning (retiring before 62), set Social Security to $0 since you won't receive benefits until at least 62. You can also run the calculator both ways to see how much Social Security changes the picture.

How much should I save for retirement each month?

A common guideline is 15-20% of gross income. But the right amount depends on your age, goals, and current savings. If you're starting at 25 and want to retire at 65, saving 15% with employer matching is usually enough. Starting at 35? You'll likely need 20-25%. For FIRE at 45, you may need 50%+ savings rates. This calculator helps you find the exact number.

What return rate should I assume?

For a diversified portfolio, 6-8% is a reasonable long-term assumption after fees. The S&P 500 has returned about 10% historically, but a retirement portfolio typically includes bonds too. Be conservative — it's better to have more than expected than to run short. After subtracting 2.5% inflation, a 7% nominal return becomes about 4.5% real return.

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