02. Kalkulator finansowy

// Wzór na ratę annuitetową
function calculateMonthlyPayment(principal, annualRate, months) {
  const monthlyRate = annualRate / 100 / 12;
  if (monthlyRate === 0) return principal / months;
  return (
    (principal * monthlyRate * Math.pow(1 + monthlyRate, months)) /
    (Math.pow(1 + monthlyRate, months) - 1)
  );
}

// Wzór na procent składany
function calculateFutureValue(principal, monthlyContribution, annualRate, months) {
  const r = annualRate / 100 / 12;
  const fvPrincipal = principal * Math.pow(1 + r, months);
  const fvContributions = r > 0
    ? monthlyContribution * (Math.pow(1 + r, months) - 1) / r
    : monthlyContribution * months;
  return fvPrincipal + fvContributions;
}