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Finance & InvestmentEntry № 01.17Documented Formula

Retirement Corpus & FIRE Calculator

Calculates financial independence corpus using the 4% rule, projected living expenses, inflation, and required monthly SIP accumulation.

Popular Searches:How much corpus is required to retire at age 45 or 50?How the 4% safe withdrawal rule works with inflationMonthly SIP required to achieve ₹5 Crore retirement corpusLean FIRE vs Fat FIRE number calculation
Financial Independence, Retire Early (FIRE) Engine
$50,000.00 / mo
$
FIRE Blueprint
Target FIRE Number (Corpus)
$40,391,591.79
Needed at age 45 (17 years from now)
Monthly SIP Needed$60,473.62 / mo
Future Monthly Expense$134,638.64 / mo
Corpus = Annual_Expense_at_FIRE / SWR (4%)
Mathematical Proof & FormulaStandard Mathematical Notation

How This Calculation Formula is Formulated

The FIRE (Financial Independence, Retire Early) corpus is based on the Trinity Study's Safe Withdrawal Rate (SWR) model (traditionally 4%, or 25x annual expenses). Future expenses are adjusted for inflation up to retirement age, and the required monthly SIP is computed to bridge the gap from zero.

Standard Algebraic Representation
\text{Corpus} = \text{Annual Expense}_{\text{at FIRE}} \times \frac{1}{\text{SWR}}
Documented algebraic formula with transparent derivation and reference notes.

Variable Definitions & Measurement Units

E_0
Current Monthly Expenses
Baseline essential and discretionary monthly living costs
i
Inflation Rate
Annual consumer price inflation (typically 5%–7% in emerging markets)
t
Years to Retirement
Target FIRE age minus current chronological age
SWR
Safe Withdrawal Rate
Percentage of portfolio withdrawn annually in year 1 (typically 3.5%–4%)
r
Pre-Retirement Return
Expected portfolio compounding rate during wealth accumulation phase
Step-by-Step Calculation Example

Retiring in 15 Years on Current Monthly Expenses of ₹50,000 (6% Inflation, 4% SWR)

Current Monthly Expense:₹50,000 (₹6,00,000/year)Inflation:6.0% p.a.Time to FIRE:15 Years
1
Future Annual Living Expense
₹6,00,000 × (1 + 0.06)¹⁵ = ₹6,00,000 × 2.39656 = ₹14,37,935 / year
Inflation more than doubles living expenses in 15 years.
2
FIRE Corpus (4% Rule / 25x Multiplier)
₹14,37,935 / 0.04 = ₹3,59,48,375 (~₹3.6 Crore)
Capital required to sustain indefinite 4% withdrawals.
3
Monthly SIP Required at 12% Return
SIP = ₹3.59 Cr / AnnuityFactor(12%, 180 mo) = ₹71,980 / month
Monthly investment needed to reach target.
Conclusion: You require a target FIRE corpus of ₹3.59 Crore in 15 years, achievable with a monthly SIP of ₹71,980.
In-Depth Editorial Analysis

The 4% Safe Withdrawal Rule & Sequence of Returns Risk

The 4% rule originated from the 1998 Trinity Study, which found that a 50/50 stock/bond portfolio sustained a 30-year retirement 95% of the time when withdrawing 4% initially and adjusting for inflation each subsequent year.

For early retirees seeking 40- to 50-year retirements, financial planners recommend a conservative SWR of 3.25% to 3.5% (28x to 30x annual expenses) to insulate against severe sequence-of-returns drawdowns early in retirement.

Frequently Asked Questions

Frequently Asked Questions About Retirement Corpus & FIRE Calculator

What is the difference between Lean FIRE, Fat FIRE, and Coast FIRE?

Lean FIRE covers bare survival expenses (basic shelter/food). Fat FIRE allows a luxurious lifestyle with travel and high discretionary spending. Coast FIRE is having enough invested early that compounding alone reaches full retirement without further savings.

Does the 4% rule work in India and high-inflation economies?

Because inflation in India is typically 5%–7% (higher than US 2%–3%), financial advisors suggest targeting 30x to 35x annual expenses (a 3.0%–3.3% SWR) and maintaining 60% equity exposure post-retirement.

How does healthcare inflation affect FIRE planning?

Medical inflation often runs at 10%–14% per year, much higher than general CPI. Ensure you carry comprehensive private super top-up health insurance alongside your liquid FIRE corpus.

Should home equity be counted towards the liquid FIRE number?

No. Your primary residence does not generate cash flow to pay grocery bills. Only liquid, yield-bearing assets (mutual funds, stocks, bonds, rental properties) should be counted in your FIRE corpus.

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Deterministic Precision & 100% Client-Side Privacy

All calculations execute in your local browser using IEEE 754 double-precision floating-point arithmetic. Your figures and financial metrics remain private and are never uploaded or saved to any cloud servers.