20/4/10 Car Affordability Rule

Loans & Borrowing
Updated Apr 2026 • Has calculator

The maximum car price you can afford: 20% down, 4-year loan, monthly payment under 10% of gross income.

What is 20/4/10 Car Rule?

The 20/4/10 rule is a car affordability guideline with three constraints: put at least 20% down to avoid being underwater; finance for no more than 4 years to limit interest paid; and keep total monthly vehicle expenses (payment plus insurance) below 10% of gross monthly income. The rule is conservative by design—it prevents car payments from crowding out savings and investment. Many Americans violate all three rules simultaneously, contributing to significant wealth drag.

Formula

Max Car Price = PV(10% monthly income, 4yr, rate) ÷ (1 − Down%)

Worked Example

Worked example — Car buyer with $75,000 income — 2024

2024

Step 1  Gross annual income: $75,000 | Monthly income: $6,250
Step 2  Max monthly payment: 10% × $6,250 = $625
Step 3  Auto loan: 7.0% rate, 48-month term
Step 4  Max loan = PV of $625/mo at 7% for 4 years ≈ $25,654
Step 5  With 20% down: max car price = $25,654 ÷ 0.80 ≈ $32,068
Step 6  → The average new car price in 2024 was $48,000 — far above this limit

Source: Edmunds — The 20/4/10 Rule for Car Buying (2024-01-01)

Calculate 20/4/10 Car Rule

Pre-tax annual income from all sources

Annual interest rate on the car loan (Experian avg: 6.7% new, 11.3% used Q1 2024)

Down payment as % of car price (rule requires ≥20%)

Maximum Car Price

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Not investment advice.

How to Interpret 20/4/10 Car Rule

< 15000
Modest — consider used vehicles in this range
15000 – 30000
Standard — new economy or used mid-range cars
30000 – 50000
Upper range — check 10% income rule carefully
> 50000
Luxury — only affordable at higher income levels
Sources
  1. Edmunds — How Much Car Can You Afford?
  2. Investopedia — 20/4/10 Rule
  3. Experian — State of the Automotive Finance Market Q1 2024