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. 47 Financing
Getting Out of a Car Lease Early: What It Actually Costs
Trading in, turning in, or buying out a lease before term. The four exit routes ranked by what they cost, why equity is only half the math, and the one route that quietly saves you the sales tax.
Read the post → - No. 46 Financing
How to Get Out of an Upside-Down Car Loan
Five routes out of owing more than your car is worth, ranked by what they actually cost — plus the two 'solutions' that make the hole deeper.
Read the post → - No. 45 Financing
Negative Equity on a Car, Explained for Beginners
What 'underwater' and 'upside-down' actually mean, why it happens to careful people, and how to tell where you stand in about five minutes.
Read the post → - No. 44 Financing
The Risks of Rolling Negative Equity Into a New Loan
Beyond the extra interest: what can actually go wrong once old car debt is financed into a new loan — from a totaled car to a denied refinance to a hole that compounds every trade.
Read the post → - No. 43 Financing
Rolling Negative Equity Into a New Loan: Pros and Cons
An honest ledger. Three situations where financing the shortfall is defensible, five where it isn't, and the test that separates them.
Read the post → - No. 42 Financing
Rolling Upfit Costs Into an Auto Loan: What It Actually Costs
Financing the service body with the truck is the easy default. Here's the arithmetic on what that convenience costs, and when a shorter equipment note at a higher rate beats it outright.
Read the post → - No. 41 Running Costs
The 2026 IRS Mileage Rate Changed Mid-Year — Here's How to Split Your Miles
The business standard mileage rate went from 72.5¢ to 76¢ on July 1, 2026. That means one year of driving gets deducted at two rates. Here's the exact split, with a worked example.
Read the post → - No. 40 Financing
Should You Pay Cash or Finance a Car? The Break-Even That Decides It
Paying cash isn't automatically smart — it has an opportunity cost. Here's the one comparison that settles cash vs finance, with a worked example and a calculator.
Read the post → - 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. Updated for the 2026 rates.
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 →