Car Affordability Calculator

The 20/4/10 rule is the gold standard for car buying: put down 20%, finance for no more than 4 years (48 months), and keep total auto expenses under 10% of your gross monthly income.

To use the Car Affordability Calculator, enter your Gross Monthly Household Income, Down Payment Savings, Trade-in Value and other values. The calculator instantly computes Maximum Affordable Car Purchase Price, Recommended Max Monthly Payment (10% Rule) and more. Results update in real time as you change any input — no submit button needed.

How to Use This Calculator

Enter your Gross Monthly Household Income (e.g. 6000 in ), Down Payment Savings (e.g. 4000 in ), Trade-in Value (e.g. 2000 in ), Desired Loan Term — choose from options such as 36 Months (3 Years), 48 Months (4 Years - 20/4/10 Rule), 60 Months (5 Years), and Expected Interest Rate (APR) (e.g. 6.5 in %). Results update instantly as you type — no submit button or page reload required. Adjust any value to compare scenarios side by side.

The Formula

20/4/10 Rule:

• 20% Down Payment Minimum

• 4-Year Max Loan Term (48 Months)

• 10% Max of Gross Monthly Income for Total Auto Payment

Max Loan Financed = Payment × [(1+r)^n - 1] / [r(1+r)^n]

Max Car Price = Max Loan Financed + Down Payment + Trade-in Value

Worked Example

6,000 gross monthly income, 4,000 down payment, 2,000 trade-in, 48-month loan at 6.5% APR.

• Recommended Max Monthly Payment (10% of 6,000): 600/month.

• Max Financed Loan Amount: 25,

321.

• Maximum Affordable Car Purchase Price: 25,321 + 4,000 + 2,000 = 31,

321.

Understanding Your Result

Evaluate your result against the specific financial decision driving this calculation. Small input differences can create large output swings — run two or three scenarios (conservative, base, optimistic) to understand the range of outcomes. For decisions involving more than a month's income, validate your result against a second source or consult a certified financial planner (CFP) or CPA depending on the tax implications.