How we calculate

Every number this calculator shows is derived from the formulas below. Nothing is a black box. If you find an error or disagree with an assumption, open an issue on GitHub.

All calculations run in your browser — no data leaves your device.

FIRE Number

Your FIRE number is the corpus you need so that a sustainable annual withdrawal covers your lifestyle forever. There are two views:

Today's-money FIRE number

How much you would need if you retired today at your current lifestyle cost:

FIRE_today = Annual Expenses / (SWR / 100)

Inflation-adjusted FIRE number (what the calculator targets)

Expenses will be higher by retirement. We project them forward and divide by SWR:

Annual Expenses at Retirement = Annual Expenses × (1 + inflation)^years_to_FIRE

FIRE_target = Annual Expenses at Retirement / (SWR / 100)

Annual Expenses is the sum of your monthly living expenses (×12), annualised sinking fund costs, elder care, and milestones. Each component is inflation-adjusted before summing.

Corpus Projection

We use the standard future-value formula for a lump sum with recurring contributions:

FV = PV × (1 + r)^n  +  PMT × ((1 + r)^n − 1) / r

Where:
  PV  = current corpus (lump sum today)
  r   = annual return rate (decimal)
  n   = years to retirement
  PMT = annual SIP contribution

In Simple mode, PV and PMT come from the corpus and SIP fields directly. In Detailed mode, the calculator runs this formula for each portfolio accountat its own return rate and sums the results — giving you a per-instrument future value.

Safe Withdrawal Rate (SWR)

The SWR is the percentage of your corpus you can withdraw annually without running out of money over your projected life span. It is fully user-controlled via the slider (3% – 5%).

Inflation Adjustment

Every future-rupee amount in this calculator is a nominal figure (not real/constant-rupee). Inflation is applied in two directions:

• Growing withdrawals in drawdown: your withdrawal increases by the inflation rate each year so your purchasing power stays constant throughout retirement.
• Sinking fund costs: the replacement cost of each item is inflated to its future cost before amortising. A ₹15L car today costs ~₹26L in 10 years at 6% inflation — the annual saving amount reflects that.
• FIRE number: annual expenses are inflated to the year you retire before dividing by SWR.

Default: 6% per year— India's approximate long-run CPI average. Urban lifestyle inflation (healthcare, education, eating out) often runs 7–9%; adjust upward if your spending skews that way.

Sinking Funds (Replacement Costs)

Large irregular expenses (car, laptop, fridge) are converted to an annual saving requirement using inflation-adjusted amortisation:

Future Cost = Today's Cost × (1 + inflation)^replacement_years

Annual Saving = Future Cost / replacement_years

Sinking fund annuals are added to your total annual expenses and therefore increase your FIRE number. You can remove any default item or add custom ones.

Tax Drag per Instrument

Each portfolio account is labelled with a tax type. At retirement, we estimate the tax owed on the gain — and how much extra corpus you need so the net-of-tax figure still meets your FIRE number.

Portfolio Weighted Return

When you use Detailed mode and fill in multiple instruments, the calculator derives a single blended return for summary projections:

Rw = Σ (balance_i / Σ balance_j) × return_i

Only accounts with a non-zero balance are included. If no accounts have a balance, the manual "expected return" assumption from the Assumptions section is used instead.

Post-FIRE Drawdown

After you retire, the corpus earns a lower "post-FIRE return" (default 8%) while withdrawals grow with inflation each year. The year-by-year calculation is:

withdrawal_year_i  = Annual Expenses at Retirement × (1 + inflation)^i

growth_year_i      = corpus_year_i × post_FIRE_return

end_corpus_year_i  = corpus_year_i + growth_year_i − withdrawal_year_i

The simulation runs from your retirement age to your projected life span (user-set, default 85). It stops early if the corpus hits zero.

Important:the corpus used in drawdown is the calculator's projected corpus at retirement — not the FIRE number. If you retire with more than your FIRE number, the drawdown table shows the actual surplus compounding over time.

Monte Carlo Simulation

The deterministic drawdown table assumes a fixed return every year. In reality, returns are volatile. Monte Carlo runs 500 independent retirement scenarios with randomised annual returns:

annual_return_scenario = Normal(μ = post_FIRE_return, σ = 12%)

For each of 500 scenarios:
  corpus_0 = projected corpus at retirement
  For each year until life expectancy:
    withdrawal_i = expenses × (1 + inflation)^i
    r_i = sample from Normal(μ, σ)
    corpus_i+1 = corpus_i × (1 + r_i) − withdrawal_i
    if corpus_i+1 ≤ 0: scenario failed, record depletion age

Income & SIP Growth

Your income (and SIP contribution) will likely grow over time. The "Annual salary/income growth" slider applies compound growth to your SIP in the corpus projection:

SIP_year_i = SIP_today × (1 + salary_growth)^i

Corpus at year n = FV using growing SIP (step-up SIP)

Internally, the years-to-FIRE calculation iterates year by year with a growing annual contribution until the corpus crosses the FIRE number:

corpus_year_i+1 = corpus_year_i × (1 + r) + SIP_year_i

Stop when corpus_year_i ≥ FIRE_target

Life Events

One-time or recurring income/expense events (home purchase, inheritance, EMI ending) are layered on top of the base projection. In the year-by-year simulation:

life_event_impact_year_i = Σ (event.amountPerYear for all active events in year i)
  — positive for income events, negative for expense events

corpus_year_i+1 = (corpus_year_i + SIP_year_i + life_event_impact_year_i) × (1 + r)

Events with inflation adjusted checked have their amount grown at the inflation rate each year. A one-time event (startAge = endAge) applies only in that single year.

Car TCO Calculator

The Car vs. Cab tool computes the true yearly cost of ownership (TCO):

C_year = D/L + (EMI × 12) + F + M + I − R/L

Where:
  D   = down payment (opportunity cost, invested at Nifty 50 CAGR)
  L   = loan tenure in years
  EMI = monthly EMI
  F   = annual fuel cost  (km/day × 365 × cost_per_km)
  M   = annual maintenance (₹12,000 base, scaled by car age and type)
  I   = annual insurance premium
  R   = residual value at end of period (depreciation curve)

Opportunity cost of down payment

The down payment is not free money — it has an opportunity cost. We compound it at a user-adjustable CAGR (default 12%, Nifty 50 long-run) over the ownership period:

OppCost = DownPayment × ((1 + CAGR)^years − 1)

Break-even km/day

The break-even is the daily kilometres at which annual car fixed costs equal the saving from driving instead of cabbing (the difference in variable cost per km):

fixed_annual = down_payment/years + EMI×12 + maintenance + insurance + parking + cleaning − resale/years

Break_even_km/day = fixed_annual / (365 × (cab_rate_per_km − fuel_cost_per_km))

If you drive more than this per day, the car pays for itself vs. a cab; below this, cabs are cheaper.

NGT Car Scrappage Rules (Metro India)

The National Green Tribunal (NGT) mandates end-of-life vehicle rules for metros. The tool caps effective ownership at the scrappage limit and shows a warning when you will be forced to scrap before your planned period ends.

effective_ownership = min(planned_ownership_years, scrappage_limit − vehicle_age_today)

TCO is computed over effective_ownership, not planned_ownership.

Car Reality Check — 20/4/10 Rule & Veblen Index

The Reality Check tab scores a car purchase against three independent frameworks:

20/4/10 Rule

2× Cash Rule

You should have at least 2× the car price in liquid savings/investments before buying. If you can't buy the car twice in cash, you probably can't afford it.

Veblen Index (0–100)

The Veblen Index scores how much of the purchase is status vs. utility:

Veblen = (price / annual_income × 50) + (price / net_worth × 50)
  capped at 100

Score < 30 → utility purchase
Score 30–60 → aspirational
Score > 60 → primarily status-driven

Should You Buy It? — Purchase Scoring

The Should You Buy It? tool runs any purchase through 5 rules and 2 honest questions, then combines them into a 0–100 score:

Score = 0 means the purchase is financially sound; higher score = riskier. The score also powers 5 binary rule checks (pass/fail) shown in the rules panel. Final score determines the verdict:

Remote Life Index

The Remote Life Index (in the FIRE results panel) scores your corpus against the cost of living in 16 Indian cities — 10 Tier 2 cities and 6 major metros.

Monthly surplus calculation

monthly_withdrawal = (FIRE_corpus × SWR) / 12

surplus_city = monthly_withdrawal − city.totalMonthly2p

Lifestyle match

City data sources

Monthly cost estimates are compiled from NoBroker/MagicBricks rent surveys (2025), Numbeo cost-of-living data, CPCB annual AQI averages, and Ookla internet speed data. All costs are for a couple sharing rent and utilities. Figures are updated annually.

Emergency Fund Check

The Protection section shows your emergency fund status relative to a 6-month expense target.

target = monthly_expenses × 6

gap = target − liquid_savings   (positive = shortfall, negative = surplus)

status:
  ≥ 6 months → Good (green)
  3–6 months → Build up (amber)
  < 3 months → Urgent (red)

What counts as liquid savings? Savings account, liquid mutual funds, and short-term FDs you can break in ≤1 week. EPF, PPF, NPS, and equity MFs do not count — they cannot be liquidated quickly in a genuine emergency.

Insurance Health Check

Adequate insurance is a prerequisite for FIRE — one uninsured health event can wipe out years of savings. The tool checks two covers:

Term Life Insurance

recommended_cover = annual_income × 10  (minimum for dependants)

status: adequate if term_cover ≥ recommended_cover

The 10× rule ensures your family can replace your income stream for at least 10 years (invested at 8–10% CAGR). If you have dependants, young children, or a home loan, consider 15–20× annual income.

Health Insurance

minimum_cover = ₹10,00,000 (₹10 lakhs) per family

status: adequate if health_cover ≥ ₹10,00,000

₹10L is the minimum family floater for a metro in 2025. Medical inflation is ~12%/year — a ₹5L policy bought today covers significantly less in 10 years. Early retirees should target ₹25–50L or a super top-up on a base policy.

Part-Time Income in Retirement

Many early retirees earn some income post-FIRE (consulting, freelance, rental, creative work). The Assumptions section lets you model this as a monthly figure. Crucially:

net_withdrawal_year_i = base_withdrawal_i + healthcare_withdrawal_i − post_FIRE_annual_income

where base_withdrawal_i = annual_expenses × (1 + inflation)^i

If post-FIRE income exceeds annual expenses, net withdrawal becomes zero (corpus is untouched that year). The corpus then continues compounding at the post-FIRE return rate.

Healthcare Inflation in Retirement

Healthcare costs inflate significantly faster than general CPI. The drawdown model separates healthcare into its own expense stream with a distinct inflation rate:

total_withdrawal_year_i =
  (base_expenses × (1 + general_inflation)^i)
  + (healthcare_monthly × 12 × (1 + healthcare_inflation)^i)
  − post_FIRE_income

LTCG Harvesting

Under Budget 2024, equity LTCG up to ₹1,25,000/year is tax-free. The Investments section shows a harvesting tip to quantify this benefit during your accumulation phase:

annual_tax_saved = ₹1,25,000 × 12.5% = ₹15,625/year

total_saved_over_n_years = ₹15,625 × years_to_FIRE

How to harvest: Each year, sell equity MF units with ₹1.25L of accumulated gains and immediately repurchase (same fund or switch to a similar one). This resets your cost basis, permanently eliminating tax on those gains. The actual amount is tax-saved, not additional returns — but it compounds over the accumulation period.

NPS Annuity in Drawdown

At retirement, NPS rules force a portion of your corpus into an annuity — a fixed lifelong pension. This affects your drawdown in two ways: it reduces your liquid corpus and adds regular income.

PFRDA December 2025 rules (non-govt subscribers)

nps_annuity_corpus = nps_corpus_at_retirement × 0.20   (if corpus > ₹8L, else 0)

annuity_gross_income = nps_annuity_corpus × 6%        (current market annuity rate)

annuity_post_tax     = annuity_gross_income × (1 − 0.30)  (30% slab for FIRE retirees)
                     ≈ 4.2% of annuity corpus per year

liquid_corpus_for_drawdown = projected_corpus − nps_annuity_corpus

net_withdrawal_year_i = base_withdrawal_i − annuity_post_tax − post_fire_income

Old vs New Tax Regime

The Income Tax card in the results panel computes both regimes using your actual portfolio contributions and shows which saves more tax this year.

New Regime (FY 2025-26)

taxable = gross_income − ₹75,000 (standard deduction)

Slabs: 0% up to ₹3L · 5% ₹3–7L · 10% ₹7–10L · 15% ₹10–12L · 20% ₹12–15L · 30% above ₹15L

87A rebate: if taxable ≤ ₹7L → tax = 0

Final tax = slab_tax × 1.04 (4% cess)

Old Regime (FY 2025-26)

deductions = ₹50,000 (std ded)
           + min(EPF_annual + PPF_annual, ₹1,50,000)   [80C]
           + min(NPS_annual, ₹50,000)                  [80CCD(1B) — old regime only]
           + ₹25,000                                   [80D health insurance, approximated]

taxable = gross_income − deductions

Slabs: 0% up to ₹2.5L · 5% ₹2.5–5L · 20% ₹5–10L · 30% above ₹10L

87A rebate: if taxable ≤ ₹5L → rebate up to ₹12,500

Final tax = slab_tax × 1.04 (4% cess)

Family FIRE Mode

The Family FIRE tab projects a household corpus — two people potentially retiring at different ages, with shared expenses and combined portfolios.

Spouse corpus projection

spouse_years_to_fire = max(1, spouse_retirement_age − spouse_current_age)

spouse_corpus = FV(
  PV  = spouse_portfolio_balance,
  r   = weighted_return_of_spouse_accounts,
  n   = spouse_years_to_fire,
  PMT = spouse_monthly_sip × 12
)

Household corpus

household_corpus = your_projected_corpus + spouse_projected_corpus

Each person is projected to their own retirement age using the standard FV formula. If retirement ages differ, the corpus values are added directly — no bridging adjustment is made to the corpus total, but the UI notes the bridge period.

Children cost tiers

Children are added in the Family section with a cost tier. Their monthly cost is added to total annual expenses and therefore increases your FIRE number. Three tiers:

Each child progresses through 4 phases as they age (costs sourced from Metro India 2025 data):

child_annual_cost = current_phase_monthly × 12

total_family_expenses = base_expenses + Σ child_annual_cost + elder_care + dependents + healthcare

Home Loan Affordability Analysis

The Home Loan tool runs two analyses: affordability (can you take this loan?) and worth (should you?).

EMI calculation

r   = annual_rate / 12   (monthly rate)
n   = tenure_months

EMI = P × r × (1 + r)^n / ((1 + r)^n − 1)

Affordability rules

True monthly cost of ownership

true_monthly_cost = EMI
  + (maintenance_rate × property_value / 12)
  + (property_tax_rate × property_value / 12)
  + society_charges
  − tax_benefit_per_month   (Section 24b interest up to ₹2L/yr, old regime only)

Rent vs buy break-even

For each year y:
  buying_cost_y   = cumulative EMIs + maintenance − equity_built
  renting_cost_y  = cumulative_rent × (1 + rent_inflation)^y
                  − opportunity_cost_of_down_payment

Break-even year = first y where buying_cost_y < renting_cost_y

Couples Finance Split

The Couples Split tool models three philosophies for dividing shared household expenses between two partners. All three models take the same inputs — each partner's monthly take-home income and total shared monthly expenses — and produce different contribution splits.

Model 1 — 50/50 Split

The simplest model: each partner pays exactly half the shared expenses, regardless of income.

Each partner pays = Expenses ÷ 2

Left over (A) = Income_A − (Expenses ÷ 2)
Left over (B) = Income_B − (Expenses ÷ 2)

Where
  Expenses = total shared monthly household expenses
  Income_A, Income_B = each partner's monthly take-home

Warning triggered if either partner's contribution > 80% of their income.

Model 2 — Proportional Split (Income-Ratio)

Each partner contributes their income-share fraction of total expenses. The higher earner pays more in absolute terms but the same percentage of income.

Income ratio (A) = Income_A ÷ (Income_A + Income_B)
Income ratio (B) = Income_B ÷ (Income_A + Income_B)

Contribution_A = Expenses × Income_ratio_A
Contribution_B = Expenses × Income_ratio_B

Left over (A) = Income_A − Contribution_A
Left over (B) = Income_B − Contribution_B

Where
  Income_ratio_A + Income_ratio_B = 1 (they sum to 100%)

Model 3 — Equal Guilt-Free Money

The most equitable model for large income gaps. The total household surplus (income minus expenses) is split equally so both partners end up with the samediscretionary money — eliminating the "I earn more so I have more fun money" dynamic.

Surplus        = (Income_A + Income_B) − Expenses
Equal fun money = Surplus ÷ 2

Contribution_A = Income_A − Equal_fun_money
Contribution_B = Income_B − Equal_fun_money

Left over (A) = Left over (B) = Equal_fun_money

Where
  Surplus = total household money remaining after all shared expenses
  Equal_fun_money = each partner's equal share of discretionary income

Model is feasible only when Income_A ≥ Equal_fun_money
                         and Income_B ≥ Equal_fun_money
(i.e. neither partner contributes more than 100% of their income)

Default Assumptions

Every default is a deliberate choice. Here is what we use and why:

Limitations & Disclaimers