Why Ultra-Luxury Real Estate Demands Sub-Second Web Architecture: Building ESTATES with Next.js 16

// Zero-Latency Client-Side Mortgage & Amortization Engine
// Formula: M = P * [r(1 + r)^n] / [(1 + r)^n - 1]
export function calculateMonthlyPayment({
  propertyPrice,
  downPaymentPercent,
  interestRateAnnual,
  loanTermYears,
  propertyTaxRate = 0.0125, // localized luxury property tax
  annualInsurance = 12000,   // prime estate coverage
  monthlyHoa = 2400          // concierge & enclave security
}: MortgageInput): MortgageCalculationResult {
  const downPayment = (propertyPrice * downPaymentPercent) / 100;
  const principal = propertyPrice - downPayment;
  const monthlyRate = interestRateAnnual / 100 / 12;
  const totalPayments = loanTermYears * 12;

  // Zero-latency exact mathematical amortization
  const monthlyPrincipalAndInterest =
    monthlyRate === 0
      ? principal / totalPayments
      : (principal *
          (monthlyRate * Math.pow(1 + monthlyRate, totalPayments))) /
        (Math.pow(1 + monthlyRate, totalPayments) - 1);

  const monthlyTax = (propertyPrice * propertyTaxRate) / 12;
  const monthlyInsurance = annualInsurance / 12;
  const totalMonthlyObligation =
    monthlyPrincipalAndInterest + monthlyTax + monthlyInsurance + monthlyHoa;

  return {
    monthlyTotal: Math.round(totalMonthlyObligation),
    principalAndInterest: Math.round(monthlyPrincipalAndInterest),
    propertyTax: Math.round(monthlyTax),
    insurance: Math.round(monthlyInsurance),
    hoaDues: Math.round(monthlyHoa),
    downPaymentAmount: Math.round(downPayment),
    loanAmount: Math.round(principal)
  };
}