Ask most people what it costs to drive a mile for work and they'll shrug. Ask an accountant and they'll quote you a single tidy number set by the tax authorities. But the standard rate you claim on a tax return and the actual amount each mile drains from your wallet are two very different figures — and the gap between them can quietly shape whether a job, a client, or a side hustle is even worth the drive.

This is a look at where that gap comes from, how the official rate is meant to work, and how to calculate what a mile really costs you so you can price your time, your invoices, and your vehicle accordingly.

The standard mileage rate: a useful shortcut, not the whole truth

The simplest way to account for a work vehicle is the standard mileage rate. Instead of tracking every receipt, you multiply your business miles by a fixed per-mile figure and deduct the total. The IRS standard mileage rate for business use has sat around 67 cents per mile, and rate updates are announced periodically — one recent adjustment set the business rate at 76 cents per mile for travel in a defined second-half period. Even a small bump like that adds up fast over thousands of miles.

The appeal is obvious: one number, minimal paperwork, and a defensible figure at tax time. But the standard rate is a national average designed to approximate the blended cost of owning and operating a typical vehicle. It smooths over the fact that a diesel van doing 30,000 stop-start city miles a year and a fuel-efficient hatchback cruising the motorway have wildly different real costs. The rate is a fair proxy for tax purposes. It is not a statement of what your specific car costs you.

What actually goes into a mile

To understand your true cost per mile, you have to break driving down into two kinds of expense: the costs that rise with every mile you add, and the costs you pay whether the car moves or not.

Variable costs — the ones you feel at the pump

  • Fuel or electricity. The most visible cost, and the one most people fixate on. It's also the one that swings hardest with driving style, traffic, and price volatility.
  • Tyres. They wear out on a per-mile basis. A set that lasts 30,000 miles has a very real cost you can divide across those miles.
  • Servicing and consumables. Oil, filters, brake pads, wiper blades — maintenance intervals are mileage-driven, so every mile brings the next service a little closer.
  • Wear-related repairs. The clutch, suspension components, and exhaust that eventually fail because of accumulated use.

Fixed costs — the ones that bleed quietly

  • Depreciation. Usually the single largest cost of running a car, and the one drivers most often ignore because they never see a bill for it. Every mile chips away at resale value.
  • Insurance. Higher for business use than for social and commuting cover.
  • Road tax and licensing. A flat annual charge regardless of distance.
  • Finance or lease payments. If you're borrowing to own the vehicle, the interest is a genuine cost of keeping it on the road.

The reason the standard rate exists is precisely because tallying all of this for every trip is impractical. But if you never estimate it even once, you're flying blind on one of the biggest running costs of self-employed or mobile work.

Two ways to account, one way to understand

Broadly, you have a choice between the standard mileage method and the actual expense method. With the standard method you log miles and apply the rate. With the actual expense method you total every real cost — fuel, insurance, repairs, depreciation — and deduct the business-use proportion.

For tax, one will usually work out better than the other, and which one depends heavily on your vehicle and how you use it. A cheap, efficient, high-mileage car often does well under the standard rate because the fixed number outpaces its modest real costs. An expensive vehicle with heavy depreciation and steep insurance may do better under actual expenses. The only way to know is to run both.

But here's the point that gets lost: even if you claim the standard rate on your return, you should calculate your actual cost per mile at least once. The tax figure tells you what you can deduct. The actual figure tells you whether the driving is worth doing at all.

How to calculate your real cost per mile

You don't need a spreadsheet degree. You need twelve months of honest numbers.

  1. Add up your annual variable costs. Total your fuel spend, plus a realistic allowance for tyres and servicing based on how often you replace them.
  2. Add up your annual fixed costs. Insurance, tax, finance interest, and — crucially — depreciation. For depreciation, estimate what your car was worth at the start of the year and what it's worth now; the difference is real money gone.
  3. Sum both totals to get your all-in annual cost of running the vehicle.
  4. Divide by your total annual miles to get your true cost per mile.

Do that and many drivers get a shock. Once depreciation and insurance are folded in, the real figure can land well above the headline fuel cost they had in their heads — and sometimes above or below the standard rate they've been claiming. That comparison is the whole game.

Why the true number changes your decisions

Knowing your cost per mile turns vague uneasiness into clear arithmetic.

  • Pricing jobs. If a client is 40 miles away, you can multiply that round trip by your real cost per mile and see instantly whether your quote covers the driving before it covers your time.
  • Choosing a vehicle. A cheaper car with punishing depreciation and thirsty running costs can be more expensive per mile than a pricier, efficient one. The sticker price lies; the per-mile figure doesn't.
  • Deciding when to drive at all. Some low-value trips simply don't pay once you count the vehicle. Seeing that in black and white helps you batch errands, decline distant low-margin work, or pass the true cost on.
  • Reimbursement fairness. If an employer or client reimburses at a set rate, you can check whether it actually covers what the driving costs you.

The record-keeping problem

All of this depends on data, and data is where good intentions die. You cannot compare the standard method against actual expenses, or work out your real cost per mile, if you don't have a reliable log of business miles and a record of what maintenance you paid for and when.

The old approach was a paper logbook in the glovebox, dutifully filled in for a week and then abandoned. The reality is that reconstructed mileage from memory is both inaccurate and hard to defend if a tax authority ever asks. Apps make this far less painful — this blog is run by the team behind Rienly, which tracks mileage automatically and keeps you on top of your vehicle's maintenance schedule, so the numbers you need for both tax and true-cost calculations are already sitting there when you want them.

Whatever tool you use, the habit matters more than the method: capture business trips as they happen, keep every service and repair receipt, and note your odometer at the start and end of the tax year.

Putting it together

The cost of driving for work isn't one number — it's a layered thing. There's the tax figure, which is a fair, low-effort approximation set for you. And there's the true figure, which is personal to your car, your mileage, and your depreciation, and which the tax rate was never designed to reveal.

Claim whichever method leaves you better off at tax time; that's simply sound accounting. But don't confuse the deduction with the truth. Once a year, sit down and work out what a mile actually costs you. Fold in the fuel, yes, but also the tyres, the servicing, the insurance, and the depreciation that no one sends you an invoice for. The resulting number is one of the most useful figures in your business — because every mile you drive for work is a decision, and now you'll know exactly what it's worth.