Lean FIRE Calculator
Lean FIRE is achieving financial independence on a frugal budget — typically with annual expenses under $40,000 and a nest egg below $1 million. It trades a lower spending floor for earlier freedom, making FIRE accessible to people who don't earn six figures.
The math is compelling: at $25K/year expenses and 4% SWR, your Lean FIRE number is just $625,000 — achievable in 7–10 years on a median income with aggressive saving. The trade-off is less margin for error and a more constrained lifestyle. This calculator helps you determine your Lean FIRE number and timeline.
Your Lean FIRE number is $625,000 ($25,000/yr ÷ 4% SWR). At $1,500/mo savings with 7% real returns, you reach Lean FIRE in 11 years.
Formula: Lean FIRE Number = Annual Expenses ÷ Withdrawal Rate
Your numbers
Lean FIRE typically means under $40K/yr
Results
Lean FIRE Number
$625,000
$25,000/yr ÷ 4% SWR
Years to Lean FIRE
11 yrs
At $1,500/mo savings
How to use this calculator
Annual expenses (frugal) — Your expected yearly spending in retirement with a frugal lifestyle. Lean FIRE typically means under $40K/year. Include housing, food, healthcare, insurance, and essential discretionary spending. Be realistic — underestimating leads to financial stress later.
Current savings — Your total investable assets today: 401(k), IRA, brokerage, HSA. Don't include your home equity unless you plan to sell and invest the proceeds.
Monthly savings — How much you invest each month. The biggest lever for reaching Lean FIRE faster. Include employer 401(k) matches.
Expected real return — Your after-inflation annual return. 7% is common for a stock-heavy portfolio. Use 5% for a more conservative estimate.
Safe withdrawal rate — The percentage you'll withdraw annually. 4% is the classic rule. For Lean FIRE, consider 3.5% for extra safety since you have less margin for error.
Real-world examples
Single in LCOL area: $20K/yr expenses
At 4% SWR: Lean FIRE number = $500,000. Saving $1,500/month at 7% from $0: reached in ~16 years. With $50K already saved: ~12 years. This is achievable on a $50K salary with a 36% savings rate.
Couple, frugal lifestyle: $35K/yr expenses
At 4% SWR: Lean FIRE number = $875,000. At 3.5% SWR: $1,000,000. Saving $2,500/month at 7% from $0: reached in ~14 years. Two incomes make this much more achievable than solo Lean FIRE.
Ultra-lean: $15K/yr expenses (van life / house hacking)
At 4% SWR: Lean FIRE number = $375,000. Saving $2,000/month at 7% from $0: reached in ~11 years. Extreme frugality dramatically reduces the target, but healthcare costs and emergencies can derail this plan without a buffer.
Formula & Methodology
Lean FIRE Number formula
- Annual Expenses = Total yearly spending in retirement (frugal budget)
- Withdrawal Rate = Safe withdrawal rate (e.g., 0.04 for 4%)
Years to Lean FIRE (iterative)
- r = Annual investment return (decimal)
- PMT = Monthly contribution
Assumptions & limitations
- Returns are assumed constant. Real markets fluctuate significantly year to year.
- Lean FIRE has less margin for error — a major expense can be catastrophic without a buffer.
- Healthcare costs are the biggest risk for Lean FIRE. Budget generously for this category.
- Does not account for Social Security, pensions, or other income sources.
What is Lean FIRE?
Lean FIRE is achieving financial independence with a minimalist lifestyle — typically annual expenses below $40,000 and a nest egg under $1 million. It trades a lower spending floor for earlier freedom.
The trade-off: Lean FIRE leaves less margin for error. Healthcare costs, home repairs, or inflation can strain a tight budget. Many Lean FIRE adherents maintain some form of flexible income as a safety net.
Key strategies: low-cost living (LCOL areas, house hacking), maximizing tax-advantaged accounts, and keeping investment fees minimal through index funds.