The 20/4/10 rule is a fast sanity check before you ever walk into a dealership. Put at least 20% down, finance for no longer than four years (48 months), and keep your total monthly transportation cost — payment plus insurance — at or below 10% of your gross monthly income.
Why 20% down? It offsets the steep first-year depreciation so you are not immediately underwater on the loan. Why four years? Longer loans lower the payment but balloon the interest and keep you in negative equity far longer. Why 10%? It leaves room for fuel, maintenance, and the rest of your life.
Our affordability calculator bakes these guardrails in. The 'safe range' you see is anchored near the 10% target, while the maximum reflects a more aggressive 15% ceiling. Stay toward the safe range and you will rarely regret the purchase.
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