Fat FIRE Calculator: Find Your Financial Independence Target
Use this guide to understand the assumptions, inputs, results, and next steps behind the calculator.
Created by Luis Gonzalez · Last updated August 3, 2026
Fat FIRE is financial independence with a larger retirement spending budget than a lean or standard FIRE plan. This calculator estimates the portfolio size needed to support your annual expenses, the age you may reach that target, your savings rate, and the withdrawal need after Social Security begins.
With the default inputs—$100,000 annual expenses, a 3.5% withdrawal rate, $300,000 current savings, $200,000 annual income, and a 7% assumed annual return—the calculator’s Fat FIRE target is $2,857,143. It estimates a 50% savings rate and reaching the target in 14 years, at age 49. These projections depend heavily on spending, returns, and how consistently you save.
For a general independence target, compare the FIRE calculator and financial independence number calculator. The Fat FIRE beginner’s guide explains how spending assumptions shape the target.
Enter Spending, Savings, and Timeline Inputs
Annual expenses are the core input because the target is calculated from expenses and the withdrawal rate. Enter the amount you expect to spend per year in retirement, not gross income. Current savings and annual income determine how quickly the model projects you can reach the target.
The default assumptions include 3.5% withdrawal rate, 2.5% inflation, age 35, $2,500 monthly Social Security beginning at age 67, and a life expectancy of 90. The calculator projects annual savings as income minus expenses, so the default annual saving amount is $200,000 − $100,000 = $100,000.
Check whether your expense estimate includes housing, taxes, insurance, healthcare, travel, and support for family members. The retirement needs calculator can help review spending categories, while the retirement number calculator offers another way to compare a target with savings.
How the Default Fat FIRE Number Is Calculated
The FIRE number is the portfolio amount implied by annual spending and a withdrawal rate:
Fat FIRE number = annual retirement expenses ÷ withdrawal rate
The calculator converts 3.5% to 0.035, then performs:
$100,000 ÷ 0.035 = $2,857,142.86
Rounded target = $2,857,143
The calculator also shows Lean and Regular FIRE comparisons. It defines Lean expenses as 40% of the entered annual expenses and Regular expenses as 70%. With $100,000 of annual expenses, those modeled budgets are $40,000 and $70,000:
Lean target = $40,000 ÷ 0.035 = $1,142,857
Regular target = $70,000 ÷ 0.035 = $2,000,000
Fat target = $100,000 ÷ 0.035 = $2,857,143
These are calculator-defined spending tiers, not universal definitions. Your own comfortable spending level may not match the 40% or 70% assumptions.
How Savings Rate and Time to Target Work
Savings rate is the portion of gross annual income left after annual expenses, as modeled by this calculator. With defaults:
Annual savings = $200,000 − $100,000 = $100,000
Savings rate = $100,000 ÷ $200,000 × 100 = 50%
To estimate years to Fat FIRE, the calculator updates the balance once per year by applying investment growth and then adding annual savings. The default projection reaches $2,857,143 in 14 years, so the projected age is 35 + 14 = 49. This is a model result, not a guaranteed date; actual saving timing and investment returns vary.
The tool reports a post-Social Security withdrawal need of $70,000 per year. Under its assumptions, annual expenses are $100,000 and Social Security is $2,500 × 12 = $30,000 per year, so $100,000 − $30,000 = $70,000 remains to be funded from the portfolio once benefits begin. This figure does not mean Social Security begins automatically at age 67 or that the benefit estimate is guaranteed. The Social Security Administration explains benefit estimates and claiming choices at SSA.gov.
Compare Expense and Withdrawal-Rate Scenarios
A change in annual expenses or withdrawal rate can move the target by hundreds of thousands of dollars. The examples below change one or both assumptions; they are simple target calculations, not revised calculator ages.
| Annual expenses | Withdrawal rate | Target calculation | Portfolio target |
|---|---|---|---|
| $80,000 | 3.5% | $80,000 ÷ 0.035 | $2,285,714 |
| $100,000 | 3.5% | $100,000 ÷ 0.035 | $2,857,143 |
| $120,000 | 3.5% | $120,000 ÷ 0.035 | $3,428,571 |
| $100,000 | 4.0% | $100,000 ÷ 0.04 | $2,500,000 |
The 4% case produces a lower target, but a higher withdrawal rate may increase the risk that a portfolio is depleted during a long retirement or poor market sequence. A 3.5% assumption is not a guarantee of lifetime income either. Learn more about the math and assumptions in the math behind FIRE.
Next Steps for a Fat FIRE Plan
Start by validating the $100,000 annual expense estimate, then compare targets at more than one withdrawal rate. Review the projected age with conservative return assumptions and confirm Social Security using an official estimate. For a gradual path to independence, compare Flamingo FIRE and Slow FIRE with your Fat FIRE timeline.
Frequently Asked Questions
Quick answers to the questions people usually have after running the retirement calculator.
1What does Fat FIRE mean?
Fat FIRE means reaching financial independence with a relatively high planned spending level. The necessary portfolio depends on your annual expenses and the withdrawal rate you choose.
2Why is the default Fat FIRE target $2,857,143?
The calculator divides $100,000 in annual expenses by a 3.5% withdrawal rate: $100,000 ÷ 0.035 = $2,857,142.86, rounded to $2,857,143.
3Does reaching the target at 49 mean I can safely stop working then?
No. The age is a projection based on annual saving and a constant return assumption. Test lower returns, higher spending, taxes, healthcare, and a longer lifespan before relying on a date.
4Should I use a 3.5% or 4% withdrawal rate?
A lower rate raises the required portfolio but may provide more cushion; a higher rate lowers the target but can increase depletion risk. Choose scenarios based on retirement length, asset mix, flexibility, and other income rather than treating either rate as universally safe.
5Is Social Security included in the default Fat FIRE target?
The target is calculated from annual expenses divided by the withdrawal rate. The calculator separately reports the modeled post-Social Security withdrawal need, which is $70,000 under default assumptions. Do not subtract Social Security from the target unless the calculator’s method explicitly does so.
6Does the savings rate use take-home pay?
The calculator uses annual income minus annual expenses. It does not necessarily calculate after-tax savings rate, so the displayed 50% may differ from the share of take-home pay you save.
7What if my expenses change after I stop working?
A spending change alters the target directly. Recalculate with separate budgets for housing, healthcare, travel, taxes, and family support, and test a higher-expense scenario before committing to a retirement date.