The 20-4-10 Rule for Buying a Car
For many years, financial planners have often recommended a simple rule to help car buyers avoid taking on too much debt and turning their car into a financial burden. It’s the 20-4-10 rule, which focuses on three factors: the down payment, the loan term, and the ratio of car ownership costs to income.
What is the 20-4-10 formula for buying a car?
The 20-4-10 rule means that buyers should make a down payment of at least 20% of the car’s value, the loan should be paid off within no more than 4 years, and the total costs associated with owning and using the car should not exceed 10% of their income. This is considered a guideline to help buyers balance their current financial capacity with the costs they will incur for many years after purchasing the car.
In particular, a 20% down payment helps reduce the amount borrowed from the outset, thereby limiting the interest payable and reducing the risk that the remaining debt will exceed the car’s actual value. This is particularly important because cars typically depreciate over time. The larger the down payment, the lower the loan amount, which means the buyer has more financial flexibility in the event the car’s value depreciates rapidly.
The second factor is the maximum loan term of 4 years, equivalent to 48 months. A shorter loan term allows buyers to pay off the debt quickly and minimize total interest costs. In exchange, the monthly payment will be higher compared to loans with terms of 5–7 years.
Finally, the total cost of owning a car should not exceed 10% of your income. This expense includes not only the monthly payments but also insurance, fuel, maintenance, and repairs. In other words, just because a car has an affordable monthly payment doesn’t mean the buyer can actually afford to own it.
For example, for a used car with an average price of about VND 659 million, if the buyer makes a 20% down payment, the monthly installment could be around VND 12.6 million, not including other expenses. When you add in about VND 4.75 million for insurance, VND 5 million for fuel, and VND 2.5 million for maintenance and repairs, the total monthly cost could reach approximately VND 24.9 million.
According to the 10% rule, a household must have an annual income of approximately VND 3 billion to keep this monthly expense within the recommended limit.
What should you do if the 20-4-10 formula doesn’t work?
If you cannot fully meet the 20-4-10 rule, the important thing is not to try to extend the loan term just to bring the monthly payment down to a more manageable level. A 72- or 84-month loan may lower your monthly payment, but it also means you’ll pay interest for a longer period and risk still owing money on the car long after its value has significantly depreciated.
Instead of focusing solely on the monthly payment, buyers should calculate the total cost of owning a car and factor it into their overall household budget. According to financial experts, if the 10% rule is too difficult to follow, allocating about 12–15% of pre-tax income to transportation costs may be a more realistic goal for some households. However, it is important that this expense does not unduly impact other essential needs or savings.
Another way to reduce financial pressure is to lower your car-purchase budget rather than extending the loan term. Buyers may want to consider used cars that are about 3–5 years old. These vehicles are typically more affordable than new cars, while still offering relatively modern safety features and technology. At the same time, choosing a highly reliable model helps minimize the risk of incurring significant repair costs.
Essentially, the 20-4-10 rule isn’t just about determining what a reasonable price for a car should be. More importantly, it’s a way for buyers to take a comprehensive look at the total cost of car ownership, rather than focusing solely on the monthly payment. When it’s not possible to fully adhere to the rule, adjusting the car’s price, increasing the down payment, or controlling total ownership costs are often better options than extending the loan term for too long.