@mcnoble/interest/interests.js

A simple interest and compound interest calculator

function simpleInterest(principal, rate, time, timeUnit = 'years') {
    if (principal <= 0 || rate <= 0 || time <= 0) {
      throw new Error('Principal, rate, and time must be positive values.');
    }
  
    const timeInYears = convertToYears(time, timeUnit);
    return (principal * rate * timeInYears) / 100;
  }
  
  function convertToYears(time, timeUnit) {
    const unitMap = {
      years: 1,
      months: 1 / 12,
      days: 1 / 365
    };
    
    if (!unitMap[timeUnit]) {
      throw new Error('Invalid time unit. Use "years", "months", or "days".');
    }
    
    return time * unitMap[timeUnit];
  }


  function compoundInterest(principal, rate, time, frequency = 'annually') {
    if (principal <= 0 || rate <= 0 || time <= 0) {
      throw new Error('Principal, rate, and time must be positive values.');
    }
  
    const n = getCompoundingFrequency(frequency);
    const compoundAmount = principal * Math.pow(1 + (rate / (100 * n)), n * time);
    
    return parseFloat((compoundAmount - principal).toFixed(2)); 
  }
  
  function getCompoundingFrequency(frequency) {
    const frequencyMap = {
      annually: 1,
      yearly: 1,
      semiannually: 2,
      quarterly: 4,
      monthly: 12,
      daily: 365
    };
    
    if (!frequencyMap[frequency]) {
      throw new Error('Invalid frequency. Use "annually", "yearly", "semiannually", "quarterly", "monthly", or "daily".');
    }
    
    return frequencyMap[frequency];
  }
  
export { simpleInterest, compoundInterest };