The math behind car costs.
First-principles breakdowns of what a car really costs to buy, finance, fuel, and keep — each derived from scratch, honest about what it leaves out, and paired with a calculator you can run.
- No. 39 The Car Itself
EV vs Gas: How Many Miles Until the EV Pays Off?
An EV often costs more up front and less per mile. The break-even is where the fuel savings repay the price premium — here's how to find yours, with a calculator.
Read the post → - No. 38 Financing
Is 0% APR Financing Actually Worth It? (Run It Against the Rebate)
0% financing isn't free if you give up a cash rebate to get it. The honest test compares total cost both ways — here's the math, with a calculator.
Read the post → - No. 37 The Car Itself
Can My Truck Tow It? The Four Limits That Actually Decide
Tow rating isn't the limit that stops most people — payload is. Here are the four numbers (GVWR, GCWR, payload, tongue weight) and how to check them, with a calculator.
Read the post → - No. 36 Financing
How a Lease Payment Is Actually Built
A lease payment is two parts plus tax: depreciation and the money-factor rent charge. Here's the exact math, so a dealer's quote stops being a black box.
Read the post → - No. 35 Financing
The Lease-End Decision Tree: Buy, Return, or Re-Lease
Three months before your lease ends you have four options and two numbers that decide between them: the residual versus market value, and your mileage.
Read the post → - No. 34 Financing
The Money Factor, Explained: The Lease Number Dealers Hope You Skip
A lease's money factor is the interest rate wearing a disguise. Multiply it by 2,400 to read it as an APR — and catch a marked-up lease in ten seconds.
Read the post → - No. 33 Running Costs
Your Real MPG Isn't the EPA Number
The window sticker is a lab estimate. Measuring your own MPG takes one tank and tells you what driving actually costs — often 10-25% more than the sticker.
Read the post → - No. 32 Financing
Will You Blow Your Lease Mileage? The Bill Waiting at Turn-In
The average driver covers 13,500 miles a year; the average lease allows 12,000. That gap is an excess-mileage charge almost nobody budgets for. Here's the math.
Read the post → - No. 31 The Car Itself
Plus-Sizing Tires: What Changes (and What Breaks Your Speedometer)
A taller tire makes your speedometer lie and your odometer undercount. Here's the geometry, how big the error gets, and how to keep the rolling diameter honest.
Read the post → - No. 30 Running Costs
How Much Does a Road Trip Cost in Gas?
Three numbers set your road-trip fuel cost: distance, your real MPG, and gas price. Here's the formula, the mistakes that throw it off, and a calculator.
Read the post → - No. 29 The Car Itself
Which Cars Hold Their Value Best (and Worst)?
Depreciation is the biggest cost of owning a car — and it varies enormously by segment. Here's what drives resale value and how to project your own car's curve.
Read the post → - No. 28 Running Costs
Charging an EV at Home vs Public: The Real Cost Gap
Home charging often costs a third of public DC fast charging per mile. Here's where the gap comes from, what eats into it, and how to find your own per-mile cost.
Read the post → - No. 27 Running Costs
How to Calculate Your Total Car Expenses (Every Line Item)
Most 'car cost' math stops at the loan payment and gas. The real total has nine line items — and the biggest one is invisible. Here's the full list, with a calculator.
Read the post → - No. 26 Financing
The 20/4/10 Rule for Buying a Car (and When to Break It)
20% down, 4-year loan, 10% of income on car costs. It's a blunt rule that prevents the most common car-buying mistakes — here's the logic and its limits.
Read the post → - No. 25 Running Costs
Car Allowance vs Mileage Reimbursement: Which Pays You More?
A flat car allowance is taxable; an IRS-rate mileage reimbursement usually isn't. The break-even is simpler than it looks — here's the math, with a calculator.
Read the post → - No. 24 Financing
Should You Buy Your Leased Car at Lease End?
One number decides it: your car's market value minus the contract buyout price. Positive means buy, negative means walk. Here's the full math, with a calculator.
Read the post → - No. 23 Financing
How Much Car Can You Afford on a $50k, $75k, or $100k Salary?
A salary doesn't set your car budget — your take-home, existing debt, and a sane payment ratio do. Here are honest numbers by income, with a calculator.
Read the post → - No. 22 The Car Itself
New vs Used: The Depreciation Math That Decides It
Buying used isn't automatically cheaper. Here's the depreciation, maintenance, and insurance math that actually decides new vs used — and what the 'new' premium costs you per year.
Read the post → - No. 21 Financing
How to Lower Your Car Payment (5 Real Levers, Ranked)
Only five things actually move a car payment — and some 'savings' cost you more in total. Here are the levers ranked by honesty, with calculators for each.
Read the post → - No. 20 Running Costs
What It Really Costs to Drive a Mile
Gas is the cost you notice; it's rarely the biggest one. Here's the five-bucket math behind cost per mile, why depreciation dominates, and how it stacks up to the IRS rate.
Read the post → - No. 19 Financing
What a Car Loan Break-Even Is — and How to Find Yours
Refi fees, a trade-in, leasing vs buying — every car-money decision has a break-even point. Here's what the term means and how to compute the three that matter.
Read the post → - No. 18 Financing
Rolling Negative Equity Into a New Car: What It Really Costs
Owe more than your car is worth? Here's exactly what happens when a dealer rolls that shortfall into your next loan — and why it quietly digs the hole deeper.
Read the post → - No. 17 Financing
The Real Out-the-Door Price: Tax, Doc Fees, and the Markup Over Sticker
The negotiated price is never what you pay. Here's how sales tax, the doc fee, registration, and add-ons build the real out-the-door price — and where the negotiation actually is.
Read the post → - No. 16 Financing
How Much Do People Actually Save Refinancing a Car Loan?
There's no average that applies to your loan — savings depend on the rate drop and remaining balance. Three worked examples, plus a calculator that runs your exact numbers.
Read the post → - No. 15 The Car Itself
Gas vs Electric: The Four Numbers That Actually Decide It
Skip the ideology. The gas-versus-EV decision reduces to mileage, the energy-price gap, the net incentive, and resale — here's the math and a calculator.
Read the post → - No. 14 Financing
How Auto Loan Interest Actually Works (and Why the Monthly Payment Lies)
A from-scratch derivation of the auto-loan payment formula, what the dealer's monthly number hides, and the few levers that actually cut what a car loan costs.
Read the post → - No. 13 Financing
How Much Car Can You Actually Afford? (Not What the Dealer Approves)
Why loan approval is the wrong number, how to work backward from take-home pay to a real price ceiling, and the two limits that bind before a dealer ever does.
Read the post → - No. 12 Financing
Lease Buyout: When the Residual Beats the Market
Your lease contract names a buyout price. Whether to take it is one number — the equity between the all-in buyout and the car's current market value.
Read the post → - No. 11 Financing
Lease vs Buy: The Honest Math the Payment Comparison Hides
Why comparing a lease payment to a loan payment is rigged, how the money-factor model actually works, and the four numbers that genuinely decide lease versus buy.
Read the post → - No. 10 Running Costs
The Mileage Deduction: Standard Rate vs Actual Expense, Decided by Math
How the IRS standard mileage rate works, when the actual-expense method beats it, and the election trap that can lock you out of the easier option.
Read the post → - No. 09 Financing
Paying Off a Car Loan Early: When the Math Says Yes (and When It Says No)
Why an early dollar of principal is worth more than a late one, how to quantify the interest saved, and the four situations where paying ahead is the wrong move.
Read the post → - No. 08 Running Costs
The Real Cost of Fuel: Why Gallons Per Mile Beats Miles Per Gallon
Fuel is the cost you underestimate because it's paid in small amounts. Here's the per-mile math, the real-MPG gap, and why MPG is a misleading unit.
Read the post → - No. 07 The Car Itself
The Year-One Cliff: How Car Depreciation Actually Works
Depreciation is the biggest cost of car ownership and the only one that never bills you. Here's the value-curve math and why buying used skips the worst of it.
Read the post → - No. 06 The Car Itself
Tire Size and the Lying Speedometer: The Geometry Explained
How to read tire-size notation, why a different size makes your speedometer wrong, and the ±3% rule that keeps a plus-size swap safe and legal.
Read the post → - No. 05 The Car Itself
Towing: Why 'Under the Tow Rating' Doesn't Mean You're Legal
The most common towing mistake isn't exceeding the tow rating — it's blowing payload through the trailer's tongue weight. Here's the math that catches it.
Read the post → - No. 04 Running Costs
The True Cost of Owning a Car: The Six Numbers, Ranked
A first-principles breakdown of what a car actually costs per year and per mile — the six components, why depreciation dominates, and the one input that decides everything.
Read the post → - No. 03 Running Costs
What It Really Costs to Charge an EV (Including the Losses Nobody Counts)
Charging isn't free of physics. Here's the per-mile EV energy math, why the wall draws more than the battery stores, and how public charging changes everything.
Read the post → - No. 02 Financing
When Refinancing a Car Loan Actually Pays (and When It's a Trap)
The lower monthly payment alone doesn't tell you whether to refi — only interest saved and break-even on fees do. Here's the math, with a calculator.
Read the post → - No. 01 Financing
0% APR vs Cash Rebate: Which Is Cheaper, in One Calculation
The dealer forces a choice between the 0% promo on full price and a cash rebate plus market-APR financing. One arithmetic question decides it — and a calculator runs it.
Read the post →