Tools in This Collection
Car Affordability Calculator
Calculate maximum car price using the 20/4/10 rule
Auto Loan Payoff Calculator
Compare loan terms and extra payment scenarios
Trade-In Value Calculator
Estimate trade-in value vs private sale
Out-the-Door Cost Calculator
Add tax, title, registration, and dealer fees to price
Lease vs. Buy Calculator
Compare total 5-year financial outcome for leasing vs buying
Car Depreciation Calculator
Model how your car loses value over time
Car Total Cost of Ownership
Calculate true cost including insurance, maintenance, and depreciation
Car Buying Workflow: From Budget to True Cost
Smart car buying follows a sequence. Before stepping into a dealership, set your maximum budget with the 20/4/10 rule: put at least 20% down, keep the loan term to 4 years or less, and keep all car costs (payment + insurance + gas + maintenance) under 10% of monthly gross income. On a $60,000 income, that means no more than $500/month total for car expenses.
Step 1: Set Your Affordability Ceiling
The Car Affordability Calculator shows the maximum car price that fits your income and down payment under the 20/4/10 rule. If you can put $6,000 down on a 48-month loan at 7% APR, a $25,000 car costs roughly $450/month — close to the limit for a $54,000 income. Start here before looking at specific vehicles.
Step 2: Compare Loan Terms
The Auto Loan Payoff Calculator shows total interest paid under different term lengths. A $25,000 loan at 7% for 48 months costs $1,868 in interest. The same loan stretched to 72 months saves $63/month but costs $3,360 total — nearly double the interest. Extra payment scenarios show how much you save by putting an extra $100/month toward principal.
Step 3: Know Your Trade-In Value
The Trade-In Value Calculator estimates what dealers are likely to offer based on your vehicle's age, mileage, and condition. Dealers typically offer 10-15% below private sale value. If the private sale estimate is $12,000, expect trade-in offers around $10,200-$10,800. Knowing this prevents low-ball surprises at the dealer.
Step 4: Calculate Out-the-Door Price
The Out-the-Door Cost Calculator adds sales tax (typically 5-10% depending on state), title and registration fees ($50-$400), and dealer doc fees ($500-$1,500) to the negotiated vehicle price. A $28,000 negotiated price in a 8% sales tax state with $1,200 in fees comes to $31,440 out the door — not $28,000.
Step 5: Compare Lease vs. Buy
The Lease vs. Buy Calculator compares total financial outcome over 5 years. Leasing a $35,000 car with a 55% residual at $350/month costs $21,000 over 3 years with no equity. Buying the same car and keeping it 7 years after payoff gives 2 years of no payment — the crossover typically occurs around year 4-5.
Step 6: Understand True Ownership Cost
The Car Total Cost of Ownership Calculator adds insurance ($1,500/yr average), maintenance ($800/yr), fuel ($2,400/yr at 12,000 miles, 30 MPG, $3.50/gal), and depreciation to your financing cost. A $30,000 car depreciating 15% annually plus $4,700 in running costs totals roughly $9,200/year in the first year — far more than the loan payment alone suggests.
Frequently Asked Questions
What is the 20/4/10 rule for car buying?
The 20/4/10 rule recommends putting at least 20% down, keeping the loan term to 4 years maximum, and keeping total car costs (payment + insurance + fuel + maintenance) under 10% of your monthly gross income. It prevents being car-poor and minimizes interest paid over the loan term.
How do I negotiate the out-the-door price at a dealership?
Ask for the out-the-door price — the total including tax, title, registration, and dealer fees — before agreeing to any number. Never negotiate on monthly payment alone. Dealers can extend the loan term to hit a monthly payment target while increasing total cost. The Out-the-Door Cost Calculator shows all components so you know what's reasonable in your state.
Is it better to lease or buy a car?
Leasing makes sense if you value lower monthly payments and driving a new car every 3 years. Buying is better financially if you keep the car 5+ years after payoff — you eventually have no monthly payment. The Lease vs. Buy Calculator compares total 5-year cost using actual quote numbers, accounting for residual value, money factor, and mileage overages.
What does a car dealer typically offer for a trade-in vs. private sale?
Dealers typically offer 10-15% below private sale value, because they need profit margin to resell the vehicle. On a car worth $12,000 privately, expect dealer offers of $10,200-$10,800. If the difference between private sale and trade-in is large and you have time, private sale puts more money in your pocket.