The 20/4/10 Rule for Car Buying

The 20/4/10 rule is a simple guideline that helps you make smart car financing decisions and avoid overspending on a vehicle.

What is the 20/4/10 Rule?

20% Down Payment

Put at least 20% down on your vehicle purchase. This helps you:

Avoid being underwater on your loan (owing more than the car is worth)
Reduce your monthly payments
Pay less interest over the life of the loan
Build equity in your vehicle from day one

4-Year Maximum Loan Term

Finance your car for no more than 4 years (48 months). Here's why:

Shorter loans mean less total interest paid
You'll own your car sooner
Reduces the risk of being upside-down on your loan
Aligns with the vehicle's depreciation curve

10% of Gross Income

Keep all vehicle expenses (payment, insurance, maintenance) under 10% of your gross monthly income. This ensures:

You can comfortably afford your car without financial stress
You have money left for other important expenses and savings
You're not house-poor (or in this case, car-poor)
You maintain financial flexibility

Example Application

Let's say you earn $60,000 per year ($5,000/month gross):

Maximum monthly car expenses: $500 (10% of $5,000)
If insurance is $150 and maintenance is $75: You have $275 for your car payment
With a 4-year loan at 6% APR and 20% down: You can afford a car around $13,000-$14,000

Why Follow This Rule?

Avoid Negative Equity: Cars depreciate quickly. A 20% down payment helps ensure you won't owe more than the car is worth.
Financial Flexibility: Keeping car costs at 10% leaves room in your budget for emergencies, retirement savings, and other goals.
Lower Total Cost: Shorter loan terms and larger down payments mean less interest paid over time.
Peace of Mind: Following conservative guidelines reduces financial stress and buyer's remorse.

When to Break the Rule

While the 20/4/10 rule is a solid guideline, there are situations where you might need to deviate:

If you have minimal expenses and can afford higher payments
If you're buying a certified used car with a great warranty
If you have a large trade-in that reduces your loan amount significantly
If interest rates are extremely low (making longer terms more acceptable)

However, always be honest with yourself about what you can truly afford!

Use Our Calculator

Our car affordability calculator automatically applies the 20/4/10 rule to help you determine how much car you can safely afford based on your income.

Calculate What You Can Afford