Most bad purchases survive the checkout because the question being asked — "can I afford this?" — is the wrong question. Almost everyone reading this can afford a $300 gadget. The right question is what each actual use of the thing will cost, and that one is brutal, because it makes you estimate a number nobody wants to say out loud: how many times you'll honestly use it.
The formula fits on a sticky note:
Cost per use = (purchase price + operating costs − realistic resale value) ÷ honest lifetime uses
Every word is load-bearing. Operating costs, because a truck isn't its sticker price. Resale, because good tools give money back. Honest, because the whole system fails on the optimistic-you who claims he'll smoke a brisket every weekend forever.
Worked examples, real prices
| Purchase | Cost basis | Honest uses | Per use |
|---|---|---|---|
| $25 Estwing hammer, decades of use | $25 | 500+ | ~$0.05 |
| $180 cordless drill kit, homeowner | $180 – $40 resale | 200 over 10 yrs | ~$0.70 |
| $400 gas pressure washer, 6 uses/yr | $400 + fuel – $150 resale | 60 over 10 yrs | ~$4.75 |
| $650 smoker used “every weekend” (really 8×/yr) | $650 + pellets – $200 resale | 40 over 5 yrs | ~$14 |
| $1,100 snowblower, Ohio (12 storms/yr) | $1,100 + gas – $300 resale | 120 over 10 yrs | ~$7.50 |
| $32,000 used pickup for 2 hauls/month | see below | $50–$90/haul |
Street prices August 2026; resale values are conservative Facebook Marketplace going rates. The pickup line is unpacked in the hauling article — it deserves its own ledger.
Read down the right column and the pattern jumps out: the hammer is free, the drill is cheap, and the aspirational purchases — the smoker, the truck-as-occasional-hauler — cost more per use than renting, hiring, or ordering the brisket from the good barbecue place. That's not an argument against smokers. It's an argument against buying one before your usage history proves you'll feed it. The full breakdown of that last line lives in truck vs. trailer vs. rental van, and it's the most expensive version of this mistake American men make.
The curve that explains everything
Cost-per-use isn't linear — it collapses. The first use of a $300 tool costs $300. The tenth costs $30 each. By use fifty it's pocket change.
That dashed line gives you the rental threshold, and it's the most practical output of the whole exercise: divide purchase price by the local rental rate, and that's the number of uses where owning starts winning. A $300 tile saw against $50/day rental: six uses. Renovating one bathroom? Rent. Flipping houses? Buy. A $6,000 mini-excavator weekend habit? That's why rental yards exist.
Resale is half the formula
Most people who try cost-per-use forget the subtraction, and it changes verdicts. A $400 pressure washer that sells used for $150 three years later didn't cost $400 — it cost $250 plus fuel. Durable, brand-name, mechanically simple things hold value: gas equipment, hand tools, cast iron, welted boots (resoled), firearms-safe categories like tool chests. Things that hold nothing: electronics more than two generations old, particleboard anything, exercise equipment in January's resale market (everyone's quitting at once), and any tool with a proprietary dead battery.
This is also the honest defense of buying quality that the sticker price hides. The cheap drill has no resale — nobody buys a used $40 drill for more than $10. The brand-name kit reliably returns 25–40% of its price on Marketplace years later. Run both through the formula with the subtraction and the price gap at the register often shrinks to almost nothing per use. The used market is effectively a rebate program for people who buy things other people want.
The discipline it imposes is nice, too: knowing you'll sell it someday makes you keep the box, the manual, and the tool itself in sellable shape. Guys who think in resale own cleaner garages. It's spooky.
The subscription test — same math, running backward
Cost-per-use has a mirror image that audits money you're already spending: recurring costs divided by actual uses. The $50/month gym visited three times in February is $16.67 a workout — information you can act on, either by going more or by admitting the $600/year truth and building the garage setup. The $89/year warehouse-club membership needs roughly $450 in genuine savings to beat its fee; a household that shops there weekly clears that easily, and the guy who went twice last year doesn't. Streaming stacks, roadside memberships, the boat club — same division, same discomfort.
Run it annually, in January, with last year's real numbers. Anything whose cost-per-use embarrasses you gets one season to improve or gets cancelled. Subscriptions bet on your amnesia; the formula is the antidote.
When the number lies
Run the formula mechanically and it will occasionally steer you wrong. Three known failure modes:
It ignores availability. A generator's cost-per-use looks absurd — you might use it twice a decade. But you're not buying uses, you're buying the outage where every rental in three counties is gone. Emergency gear gets judged against the cost of the emergency, not the frequency — the logic behind the $500 car kit. Insurance-type purchases sit outside the formula. Just be honest about which purchases genuinely qualify; the smoker does not.
It ignores quality thresholds. Dividing by uses assumes the uses are equivalent. The cheap version failing mid-use can cost more than the price gap — a stripped fastener, a ruined workpiece, a Saturday. That adjustment is the entire subject of the buy-it-for-life ledger, and the short rule from the Harbor Freight comparison applies: weight the formula by what a failure costs, not just what a replacement costs.
It ignores your time. If renting means two 40-minute round trips to the counter every single use, price your hours into the rental side. Sometimes the $300 tool is really buying back six Saturdays' worth of errands, and at any reasonable value on your time, that math clears easily.
Getting the "uses" number honestly
The formula's weak joint is the denominator, because it comes from the least reliable source available: you, at the moment of wanting something. Three ways to harden it. Use history, not intention — you didn't smoke a brisket last year with the borrowed smoker access you had, so the number for the $650 smoker is built on eight, not fifty-two. Check your receipts — your card history knows how many times you paid for the thing the purchase supposedly replaces; four car washes last year does not support a $300 detailing rig. Apply the two-season rule for anything over about $400 — want it across two seasons, borrowing or renting it meanwhile, before buying. Wants that survive six months of renting are real; the rest were weather. None of this is complicated. All of it is mildly insulting to the version of you holding the credit card, which is exactly the point.
Make it a habit
The 2-minute checkout ritual (anything over ~$75)
- Write the real cost: price + consumables + accessories − what it'll sell for used. Cars: add fuel, insurance, maintenance — the average new vehicle runs about $11,577 a year all-in, per AAA's ownership-cost data, which is a cost-per-use lesson all by itself.
- Count last year's actual uses of the thing it replaces or the job it does. Not projected uses — historical ones. Your past behavior is the only honest forecast you own.
- Divide. Compare against renting, borrowing, or paying someone.
- If the number's ugly but you still want it, buy it — knowingly. This is a math habit, not a monastery.
Cost-per-use won't tell you what to want. It tells you what wanting it costs, in units you can't negotiate with. Run it for a month and you'll notice the pattern I did: the boring, constantly-used stuff — hammers, boots, the washer — is nearly free per use, and the impressive stuff idles. Buy accordingly, and the garage fills up with things that earn their space.