I Built an All-in-One Estate Tax & Islamic Inheritance Calculator in Vanilla JS

Calculating complex financial data across global tax exemptions and religious frameworks (Fara'idh) usually requires heavy backend systems. I challenged myself to build a 100% client-side, ultra-fast Estate Tax & Inheritance Calculator using pure Vanilla JavaScript.

Here is how I tackled the core calculations, handled complex edge cases, and built the tool.

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⚡ The Challenge & Core Logic

The tool needs to handle two distinct financial logic engines simultaneously:

1. Federal & State Estate Tax Calculations:

   • Taxable Estate = Gross Estate - Deductions - Lifetime Exemptions
   • Dynamically applies state-level exemptions and bracket rates.

2. Islamic Inheritance (Fara'idh) Distribution Engine:

   • Automatically calculates legal fixed shares (Fard) for surviving heirs.
   • Accounts for debts, funeral expenses, and valid bequest limits (Wasiyyah capped at 1/3).

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💻 Core JS Calculation Snippet

Here is a quick look at the core JS function that powers the client-side engine:

javascript
function calculateEstateTax(grossAssets, debts, exemptions, stateRate = 0) {
  const netEstate = Math.max(0, grossAssets - debts);
  const taxableAmount = Math.max(0, netEstate - exemptions);

  // Base federal tax estimation (top rate standard)
  const federalTax = taxableAmount * 0.40;
  const stateTax = taxableAmount * stateRate;

  return {
    grossEstate: grossAssets,
    taxableEstate: taxableAmount,
    totalTaxDue: Math.round(federalTax + stateTax)
  };
}
Live demo:

    

        

          
            
          
        
      

        

          
            Estate Tax & Inheritance Calculator 2026 
          
        
          
        

            
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