GuideCalculatorDetailed Guide

How to Build a Auto Loan Calculator

An auto loan calculator estimates monthly car payments based on price, down payment, interest rate, and loan term. Helps buyers understand total cost and compare financing options.

What is a Auto Loan Calculator?

Auto loans typically have shorter terms (36-72 months) and higher rates than mortgages. Trade-in value and down payment reduce the financed amount. Understanding total cost helps avoid being 'upside down' on a loan.

The Formula

Monthly Payment = P[r(1+r)^n] / [(1+r)^n - 1]
Financed Amount = Vehicle Price - Down Payment - Trade-in Value
Total Cost = (Monthly Payment × Months) + Down Payment

Code Example

JavaScript

function calculateAutoLoan(vehiclePrice, downPayment, tradeIn, annualRate, months) {
  const principal = vehiclePrice - downPayment - tradeIn;
  const monthlyRate = annualRate / 100 / 12;

  if (monthlyRate === 0) {
    return { payment: principal / months, principal, totalCost: principal + downPayment };
  }

  const payment = principal *
    (monthlyRate * Math.pow(1 + monthlyRate, months)) /
    (Math.pow(1 + monthlyRate, months) - 1);

  return {
    payment: Math.round(payment * 100) / 100,
    principal,
    totalInterest: (payment * months) - principal,
    totalCost: (payment * months) + downPayment
  };
}

How to Build It

1
Create inputs for vehicle price, down payment, and trade-in value
2
Add interest rate and loan term selectors
3
Calculate monthly payment and total cost
4
Show interest vs principal breakdown
5
Add comparison for different terms/rates

Key Features to Include

Trade-in value integration

Multiple term comparison (36, 48, 60, 72 months)

Total cost of ownership view

Dealer vs bank rate comparison

Depreciation impact visualization

Monetization Strategies

Auto lender affiliate partnerships

Lead generation for dealers

Insurance cross-sell

White-label for car shopping sites

Recommended Tech Stack

Frontend

React with term comparison sliders

Backend

Rate API for current market rates

Hosting

Vercel or Netlify

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