Entry № 11 · logged Sep 29, 2026
Car Affordability Calculator Form CA-11
The dealer sells you the monthly payment. The ledger works the other way: your income in, the max sticker price out. Pick the rule — the strict 20/4/10 or the practical 15% — type your numbers, and the slip posts the price that fits, with insurance and fuel counted as real lines, not footnotes.
Buyer’s slip, Form CA-11. Tab one solves your income backwards into a max price. Tab two prices a specific car’s loan and stamps whether it fits the rule. Both count the true monthly cost — payment, insurance, fuel — never the payment alone.
Term is yours to choose under the 15% rule.
Prefilled at 7% APR, the going neighborhood for a good-credit auto loan in Sep 2026 — replace it with your actual quote. Take-home default assumes roughly 25% off the top for taxes on $75,000; type your real number.
The verdict checks the true monthly cost — payment plus insurance and fuel — against 15% of the take-home you type.
Posted entry · Form CA-11
More doors into the same ledger Form CA-11
Every angle on the car question, same arithmetic underneath:
- The $60k salary checkstrict approves $13,050; practical approves $33,407
- The $75k salary checkstrict approves $19,575; practical approves $40,513
- The $100k salary checkstrict approves $30,450; practical approves $52,346
- The loan payment calculator$22,000 at 7%: $435.63 a month, $4,138 in interest
- The 20/4/10 rule, explainedthe three lines and what they cost you on $75k
How the ledger prices a car Form CA-11
A car payment is one line of a five-line stack. The loan line comes from the same amortization formula lenders use: on a $22,000 loan at 7% for 60 months it posts $435.63 a month, and $4,138 of the $26,138 total is interest. That line never moves on a fixed-rate loan — but it is not the number that decides whether you can afford the car.
Affordability runs the other direction, and there are two honest rules. The 15% rule (Edmunds): the payment alone stays at or under 15% of your monthly take-home pay. On $75,000 of income — about $4,688 a month after roughly 25% in taxes — that is $703 a month for the payment, which at 7% for 60 months supports a $35,513 loan, or a $40,513 sticker with $5,000 down.
The 20/4/10 rule is stricter on purpose: 20% down, a 4-year maximum term, and all car costs — payment plus insurance, fuel, and upkeep — under 10% of your gross monthly income. On the same $75,000, that is a $625 total cap; with $150 of insurance and $100 of fuel set aside, $375 a month is left for the payment, which at 7% for 48 months supports a $15,660 loan — a $19,575 car with 20% down. The gap between $40,509 and $19,575 is the gap between “I can make the payment” and “this car cannot hurt me.”
The term is the lever dealers pull hardest. Stretch that $22,000 loan to 72 months and the payment drops to $375.08 — but the interest rises to $5,006 and you keep paying a full extra year on a car losing value the whole time. If you need the longer term to afford the payment, the car is too expensive. That is the whole rule, in one sentence.
Common questions Form CA-11
What is the 20/4/10 rule?
Put at least 20% down, finance for no more than 4 years, and keep your total car costs — loan payment plus insurance, fuel, and maintenance — under 10% of your gross monthly income. On $75,000 that is a $625-a-month total cap: with $150 of insurance and $100 of fuel set aside, about $375 is left for the payment, which supports a $15,660 loan at 7% over 48 months — a $19,575 car with 20% down.
Is the 15% rule about the payment or everything?
The payment. Edmunds’ rule is that the loan payment alone should be no more than 15% of your monthly take-home pay (after taxes). Their full position adds a second cap — payment plus insurance, fuel, and maintenance inside 20% of take-home. This slip prices the payment against 15% and prints the true monthly stack beside it so you can check the 20% yourself.
Why does the loan term matter so much?
A longer term shrinks the monthly payment but grows the total interest — and on a depreciating car, a 72- or 84-month loan can leave you owing more than the car is worth for years. On a $22,000 loan at 7%, 60 months costs $4,138 in interest while 72 months costs $5,050 and keeps you paying a full extra year.
Should I really put 20% down?
Twenty percent down means you start with equity instead of starting underwater — cars lose value fastest in year one, and a small down payment on a long term is how people end up owing $18,000 on a car worth $14,000. The strict 20/4/10 mode on this slip checks your down payment against 20% of the price and stamps the verdict.
Do insurance and fuel count toward what I can afford?
They have to. A $400 payment with $180 of insurance and $120 of fuel is a $700-a-month car, not a $400 one. This slip prices every verdict on the true monthly cost — payment plus the insurance and fuel lines you type — never on the payment alone.
Is this financial advice?
No. It’s amortization arithmetic on numbers you type: it doesn’t check your credit, approve loans, or know what your dealer will actually offer. A lender’s pre-approval and your own budget have the final word.