Freedom CalcsFinancial independence, with clear assumptions
Lean FIRE Calculator
A lower spending plan needs a realistic cushion. Build your essential budget, allow for uneven costs, and see how much saving the plan requires.
Example estimate
- Lean FIRE target
- $900,000
- Annual spending budget
- $36,000
- Projected assets at target age
- $753,188
- Monthly saving needed by target age
- $1,909
- First full-target milestone in this horizon
- Not reached
The projection uses 3.88% real annual growth with end-of-month contributions. Projected assets are below the target at the chosen age. The first milestone is not a promise that the portfolio remains above the target.
| Time | Projected portfolio |
|---|---|
| Age 35 | $100,000 |
| Age 36 | $122,202 |
| Age 37 | $145,266 |
| Age 38 | $169,225 |
| Age 39 | $194,115 |
| Age 40 | $219,972 |
| Age 41 | $246,833 |
| Age 42 | $274,736 |
| Age 43 | $303,724 |
| Age 44 | $333,837 |
| Age 45 | $365,120 |
| Age 46 | $397,618 |
| Age 47 | $431,377 |
| Age 48 | $466,448 |
| Age 49 | $502,881 |
| Age 50 | $540,728 |
| Age 51 | $580,046 |
| Age 52 | $620,890 |
| Age 53 | $663,320 |
| Age 54 | $707,398 |
| Age 55 | $753,188 |
Educational estimate. Taxes, fees, market volatility, account access, and later retirement withdrawals are not simulated.
How this calculator works
Lean FIRE target = (essential expenses + flexible spending + annual reserve) ÷ withdrawal rate
Real return = (1 + nominal return) ÷ (1 + inflation) − 1. The effective monthly rate is (1 + real return)1/12 − 1. All spending and income retain today’s purchasing power.
After N months, balance = starting assets × (1 + m)N + monthly contribution × [(1 + m)N − 1] ÷ m. At m = 0, balance = starting assets + monthly contribution × N. Solving this equation for the contribution gives the savings needed by the target age.
This is a deterministic illustration. The withdrawal rate sets a target, without simulating later withdrawals or estimating a safe rate. Dollar displays are rounded; calculations retain precision.
Reproduce the default example
$36,000 annual spending, $100,000 starting assets, $1,500 month-end deposits, age 35 to 55 (240 months), 7% nominal return, 3% inflation, and a 4% withdrawal assumption. Deposits maintain today’s purchasing power. These are hypothetical inputs, not a recommended budget or return forecast.
- Portfolio target = $36,000 ÷ 0.04 = $900,000.
- Real annual return = 1.07 ÷ 1.03 − 1 = 3.883495%; effective monthly return = 0.318003%.
- After 240 months, the closed-form accumulation formula gives $753,188 with the entered $1,500 deposits.
- Solving for deposits to reach $900,000 at age 55 gives $1,909 per month, rounded to whole dollars here. The calculation retains precision; rounding a deposit changes the final balance.
| Nominal / real annual return | Projected assets at age 55 | Monthly saving needed |
|---|---|---|
| 1% / -1.94% | $365,602 | $4,190 |
| 3% / 0.00% | $460,000 | $3,333 |
| 7.000000000000001% / 3.88% | $753,188 | $1,909 |
This fixed example stays separate from your live results above. Sensitivity comparisons change one assumption at a time and show model arithmetic, not historical outcomes or the chance of retirement success.
What is Lean FIRE?
Lean FIRE is financial independence built around relatively modest spending. It is a planning label rather than an official income limit or portfolio threshold. The useful question is whether the budget covers the life you expect to lead, including costs that do not arrive every month.
A lean budget can leave less flexibility when rent, insurance, or essential services rise. Check housing, transport, healthcare, taxes, and annual replacements before deciding the spending figure. A reserve is part of this yearly budget; your separate emergency fund should not be included in invested assets.
Build a target you can reproduce
The default example totals $24,000 essentials + $6,000 flexible spending + $6,000 reserve = $36,000 per year. Dividing by 4% gives $900,000. A 3% assumption raises the target to $1,200,000, while 5% lowers it to $720,000. The smaller number is not evidence of a safer plan.
For a zero real-return example, starting with $100,000 and adding $1,500 each month produces $460,000 after 20 years. Reaching $900,000 over those years would require $3,333.33 a month before rounding. You can reproduce this case by setting the same nominal return and inflation.
Stress-test an essential budget
Try increasing the essential-expense line and lowering the return assumption. Every additional $1,000 of annual spending adds $25,000 to a target calculated at 4%. This sensitivity can matter more than small changes to the tool’s displayed rounding.
The model maintains a constant real spending budget and constant real contributions. Your personal inflation can differ from a broad consumer-price measure. The annual projection helps compare assumptions, but it does not model unemployment, a housing move, medical bills, or a market crash.
Lean FIRE, Barista FIRE, and Coast FIRE
Lean FIRE lowers the total spending target; Barista FIRE uses work income alongside portfolio withdrawals. Coast FIRE is an earlier savings milestone with no portfolio withdrawals before the future retirement age. These approaches can overlap in a life plan, but they answer different calculation questions.
If part-time work will be part of the plan, use the Barista calculator to model its duration. Do not subtract temporary wages from a permanent Lean FIRE spending target without reserving for the period after that income ends.
Lean FIRE questions
Comparing tools? Read the FAQs for all five FIRE calculators for help choosing a model and keeping inputs consistent.
Is Lean FIRE suitable for every location?
A realistic lean budget depends on your housing, local costs, household size, and needs. The example is not a recommended budget or a claim that it works everywhere.
Why include a reserve in a lean budget?
Repairs and replacements can be uneven without being optional. Spreading expected irregular costs across years makes the target easier to compare with a monthly spending plan.
Does the result include benefits or tax calculations?
No. You must budget for applicable costs. This projection does not calculate Social Security eligibility, benefit timing, tax brackets, or access to retirement accounts.
Sources, limits, and maintenance
The formulas above are disclosed model arithmetic. Historical withdrawal studies provide context for the initial withdrawal assumption; they do not validate this calculator’s targets, predict future returns, or endorse our work.
- St. Louis Fed: exact real-rate conversion
Purchasing-power conversion, not a return forecast.
- William P. Bengen: Determining Withdrawal Rates Using Historical Data (1994)
Historical withdrawal research; no guarantee for this model.
- Cooley, Hubbard & Walz: Retirement Savings (1998), author-hosted copy
Historical US stocks/corporate bonds, 1926–1995, 15–30-year payouts; excludes taxes and transaction costs.
- US Bureau of Labor Statistics: CPI questions and answers
Population inflation measure; individual spending can differ.
The tool does not calculate taxes, benefits, account restrictions, fees, lifespan, or market risk. Include relevant expenses in your budget. Read the shared methodology and financial disclaimer.
How the arithmetic is checked
Tests compare monthly accumulation with the closed-form equation, including zero and negative real returns. Required deposits, equal ages, an already-reached target, and invalid inputs are checked. The repeatable example and sensitivity table are checked against the interactive calculation. These are software and arithmetic checks, separate from financial professional review.
Prepared by Freedom Calcs team. Model version 1.1.0 · Prepared and checked . Send a correction with this page URL, non-sensitive sample inputs, and the result you expected.