What the income needed for a purchase calculator does
This calculator estimates the gross income you need to comfortably afford a financed purchase — a car, appliance, or any big-ticket item you plan to pay off over time. It first works out the monthly loan payment for the amount you finance, then scales that payment up to the income required, using the share of your paycheck you are willing to commit to the payment.
How to use it
Enter the purchase price and, if you have one, a down payment. Add the financing details: the annual percentage rate (APR) and the term in months. Finally, set the largest share of your gross monthly income you want the payment to take — for vehicles, 10% is a common ceiling. The result shows the gross annual and monthly income you would need, along with the estimated monthly payment.
The formula explained
First, the financed amount is the price minus any down payment:
$$P = \text{Purchase price} - \text{Down payment}$$The monthly payment uses the standard amortization formula, where r is the monthly interest rate (APR divided by 12) and n is the number of months:
$$M = P \times \frac{r(1+r)^n}{(1+r)^n - 1}$$If the rate is zero, this simplifies to the price spread evenly across the term:
$$M = \frac{P}{n}$$The income needed is the payment divided by p, the share of gross monthly income allowed for the payment (as a decimal), converted to a yearly figure:
$$\text{Required annual income} = \frac{M}{p} \times 12$$Worked example
Suppose you buy a $30,000 car with a $5,000 down payment, financing the remaining $25,000 at 7% APR over 60 months. The monthly rate is 7% divided by 12, or about 0.5833%, which gives a monthly payment of about $495.03. If you cap that payment at 10% of your gross monthly income, you need roughly $495.03 divided by 0.10, or about $4,950 per month — around $59,404 in gross annual income to comfortably afford the purchase.
Frequently asked questions
Does this figure include taxes, insurance, or upkeep? No. It sizes your income around the loan payment on the financed amount only, so budget separately for sales tax, insurance, fuel, and maintenance.
What payment percentage should I use? For vehicles, the 20/4/10 rule suggests keeping the payment at or below 10% of your gross monthly income; choose a lower percentage to leave more room in your budget.
What if I pay cash instead of financing? This tool models a financed purchase with a recurring monthly payment. If you plan to pay cash, compare the price against your savings directly rather than sizing it against your income.
