Check 20% down, a loan of at most four years, and a 10% transportation budget using the annual loan interest rate and operating costs. You can also solve maximum car price or required annual income. Optional settings default to 20% down, 48 months, zero operating costs, and a 10% budget.

Check the 20% down, 48-month, and 10% transportation guidelines.

Include financed taxes and purchase fees in this amount; trade-in equity and rebates are not modeled separately.

Use the contract interest rate. APR also includes fees and may differ. Enter 0 for no interest.

Optional settings

The common rule uses gross income. Take-home is an alternative comparison, not a tax conversion.

Default 20%; must be below 100% for this financed-purchase model.

Default 48 months; supported range 1–120 whole months.

Default 0. Include insurance, fuel, maintenance, registration, and recurring fees.

Default 10%. Custom budgets do not change the separate 10% rule check.

Display only. Enter every monetary amount in the same currency.

20/4/10 Rule Formula

The formulas below describe the standard guideline. The calculator also models equal monthly loan payments and lets you select a custom transportation budget.

DP = CP × .20
MI = MC / .10

Variables:

  • DP is the down payment ($)
  • MI is the minimum monthly income ($)
  • MC is the total monthly transportation cost: loan payment plus insurance, fuel, maintenance, registration, and recurring fees ($)
  • CP is the car price of the wanted car ($)

The 20/4/10 guideline calls for at least 20% of the vehicle price down, a loan no longer than 48 months, and total monthly transportation costs no higher than 10% of gross monthly income. Take-home income is available as an alternative comparison. A custom budget changes the price or income solution, while the fixed 10% check remains separate.

How to Calculate 20/4/10 Rule?

The following steps outline how to calculate the 20/4/10 Rule.

  1. First, determine the car price of the wanted car ($). 
  2. Calculate down payment: DP = CP × 0.20. Use the contract interest rate, which can differ from fee-inclusive APR, to estimate the payment on the financed balance.
  3. Add monthly operating costs to the loan payment and compare that total with 10% of monthly income. Check the down-payment and term guidelines separately.
  4. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

car price of the wanted car ($) = 25,000

DP = 25,000 × 0.20 = $5,000, leaving $20,000 financed. At 6% annual interest over 48 months, the estimated loan payment is $469.70. With $300 in other monthly costs, total transportation costs are $769.70. A 10% budget requires about $92,364.07 annual income. This is a planning estimate, not a lending decision.

Calculator Change Log:

  • 6/9/25 - Added two different modes of calculation. Afford this car mode and max purchase price mode. Both modes use the 20/4/10 rule.