stockcalc-tools

Indian Financial Formulas — Open Source JavaScript Library

NPM Ready Live Tools Made for India

A curated, copy-paste-ready collection of India-specific financial calculation formulas in JavaScript. All formulas are validated and used in production at StockCalc.in — India’s most comprehensive free financial calculator platform.

MIT Licensed. No dependencies. Browser + Node.js compatible.

📦 Formula Index

Formula Section
FD Maturity →
PPF Maturity →
CAGR →
Gratuity →
GST Inclusive / Exclusive →
LTCG Tax →
Rule of 72 →
Inflation-Adjusted Returns →
NPS Corpus →

FD — Fixed Deposit Maturity

/**
 * FD Maturity Amount
 * @param {number} principal  - Deposit amount (₹)
 * @param {number} rate       - Annual interest rate (%)
 * @param {number} years      - Tenure (years)
 * @param {number} frequency  - Compounding: 1=annual, 2=half-yearly, 4=quarterly, 12=monthly
 */
function fdMaturity(principal, rate, years, frequency = 4) {
  return principal * Math.pow(1 + rate / 100 / frequency, frequency * years);
}

// Examples:
fdMaturity(100000, 7.1, 1, 4);  // SBI FD ₹1L, 1yr, quarterly → ₹1,07,262
fdMaturity(100000, 7.25, 5, 4); // HDFC FD ₹1L, 5yr → ₹1,42,814

// → Live calculator: https://stockcalc.in/calculator/fd

PPF — Public Provident Fund

/**
 * PPF Maturity after 15 years
 * Interest credited annually on minimum balance between 5th–last of month
 * @param {number} annual  - Annual deposit (₹) — max ₹1,50,000
 * @param {number} rate    - Current PPF rate (%) — 7.1% as of 2026
 */
function ppfMaturity(annual, rate = 7.1) {
  let balance = 0;
  for (let year = 1; year <= 15; year++) {
    balance = (balance + annual) * (1 + rate / 100);
  }
  return Math.round(balance);
}

ppfMaturity(150000, 7.1); // ₹40,68,209 at max contribution

// → Live calculator: https://stockcalc.in/calculator/ppf

CAGR — Compound Annual Growth Rate

/**
 * CAGR — Compound Annual Growth Rate
 * @param {number} beginValue - Initial value / investment
 * @param {number} endValue   - Final value / current value
 * @param {number} years      - Number of years
 * @returns {number}          - CAGR in % (e.g. 12.5 for 12.5%)
 */
function cagr(beginValue, endValue, years) {
  return (Math.pow(endValue / beginValue, 1 / years) - 1) * 100;
}

cagr(100000, 250000, 7); // → 13.98% CAGR

// → Live calculator: https://stockcalc.in/calculator/cagr

Gratuity Calculator

/**
 * Gratuity as per Payment of Gratuity Act, 1972
 * Applicable for employees with 5+ years of continuous service
 * @param {number} lastSalary  - Last drawn Basic + DA (₹/month)
 * @param {number} years       - Years of service
 */
function gratuity(lastSalary, years) {
  // Formula: (15/26) × Last Salary × Years
  // 15 days wages per year, 26 working days/month
  return Math.round((15 / 26) * lastSalary * years);
}

gratuity(80000, 10); // → ₹4,61,538

// → Live calculator: https://stockcalc.in/calculator/gratuity

GST Calculator

/**
 * GST — Add GST to a base price (exclusive → inclusive)
 * @param {number} amount  - Pre-GST price
 * @param {number} gstRate - GST rate % (5, 12, 18, or 28)
 */
function addGST(amount, gstRate) {
  const gst = amount * gstRate / 100;
  return { baseAmount: amount, gst, totalAmount: amount + gst };
}

/**
 * Extract GST from GST-inclusive price (inclusive → exclusive)
 * @param {number} totalAmount - Price including GST
 * @param {number} gstRate     - GST rate %
 */
function removeGST(totalAmount, gstRate) {
  const baseAmount = totalAmount * 100 / (100 + gstRate);
  const gst = totalAmount - baseAmount;
  return { baseAmount: Math.round(baseAmount), gst: Math.round(gst), totalAmount };
}

addGST(1000, 18);    // { baseAmount: 1000, gst: 180, totalAmount: 1180 }
removeGST(1180, 18); // { baseAmount: 1000, gst: 180, totalAmount: 1180 }

// → Live calculator: https://stockcalc.in/calculator/gst

LTCG — Long-Term Capital Gains Tax

/**
 * LTCG Tax on Indian Equity (post-Budget 2024)
 * Rate: 12.5% on gains above ₹1.25L (no indexation for equity)
 * @param {number} purchasePrice  - Cost of acquisition (₹)
 * @param {number} salePrice      - Sale price (₹)
 * @param {number} units          - Number of units / shares
 */
function ltcgTax(purchasePrice, salePrice, units) {
  const totalGain = (salePrice - purchasePrice) * units;
  const exemptionLimit = 125000; // ₹1.25L exempt per financial year
  const taxableGain = Math.max(0, totalGain - exemptionLimit);
  const tax = taxableGain * 0.125; // 12.5% flat
  const cess = tax * 0.04;         // 4% Health & Education Cess
  return {
    totalGain: Math.round(totalGain),
    taxableGain: Math.round(taxableGain),
    tax: Math.round(tax + cess),
  };
}

ltcgTax(500, 1200, 1000); // Bought 1000 shares at ₹500, sold at ₹1200
// { totalGain: 700000, taxableGain: 575000, tax: 74750 }

// → Live calculator: https://stockcalc.in/calculator/ltcg

Rule of 72

/**
 * Rule of 72 — How many years to double your money
 * @param {number} rate - Annual return rate (%)
 * @returns {number}    - Approximate years to double
 */
const ruleOf72 = (rate) => 72 / rate;

ruleOf72(12); // → 6 years at 12% return
ruleOf72(7.1); // → ~10.1 years at PPF rate

// → Live calculator: https://stockcalc.in/calculator/rule-of-72

Inflation-Adjusted Real Returns

/**
 * Real Return after adjusting for inflation
 * @param {number} nominalReturn - Expected return (%)
 * @param {number} inflationRate - CPI inflation rate (%)
 */
function realReturn(nominalReturn, inflationRate) {
  return ((1 + nominalReturn / 100) / (1 + inflationRate / 100) - 1) * 100;
}

realReturn(12, 6); // → 5.66% real return on equity at 6% inflation

// → Live inflation calculator: https://stockcalc.in/calculator/inflation

NPS — National Pension Scheme

/**
 * NPS Corpus at retirement
 * @param {number} monthly     - Monthly contribution (₹)
 * @param {number} annualRate  - Expected annual return (%)
 * @param {number} years       - Years to retirement
 * @param {number} annuityPct  - % of corpus used for annuity (min 40%)
 * @param {number} annuityRate - Annuity rate (%) — typically 6%
 */
function npsProjection(monthly, annualRate, years, annuityPct = 0.4, annuityRate = 6) {
  const r = annualRate / 12 / 100;
  const n = years * 12;
  const corpus = monthly * (((Math.pow(1 + r, n) - 1) / r) * (1 + r));
  const annuityCorpus = corpus * annuityPct;
  const lumpsum = corpus * (1 - annuityPct);
  const monthlyPension = (annuityCorpus * annuityRate / 100) / 12;
  return {
    corpus: Math.round(corpus),
    lumpsum: Math.round(lumpsum),
    monthlyPension: Math.round(monthlyPension),
  };
}

npsProjection(10000, 10, 30); // ₹10K/month, 10% return, 30 years
// { corpus: 22,792,459, lumpsum: 13,675,476, monthlyPension: 45,585 }

// → Live calculator: https://stockcalc.in/calculator/nps

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