Cost per Use: The Number That Decides Whether a Purchase Was Worth It
A twelve dollar pair of shoes and a ninety dollar pair of shoes look like a thirty dollar gap and a seventy-eight dollar gap depending on who is doing the looking. The only figure that settles it is cost per use, and almost nobody works it out before paying.
The formula, which is simpler than it sounds
Take the purchase price, subtract any resale or repair cost you expect, and divide by the number of times you will realistically use the item. That is it. No discounting, no inflation adjustment, no spreadsheet.
The hard part is not the arithmetic. It is being honest about the number of uses, because that is where wishful thinking enters.
People reliably overestimate use by a factor of two or three. The running shoes that will be worn four times a week get worn twice, and then the shelf holds them for a year.
Two examples that make it concrete
A cheap pair of everyday shoes at twelve dollars, worn twice a week for four months before the sole splits, works out to about thirty-seven cents per wear.
A ninety dollar pair worn twice a week for three years works out to about twenty-nine cents per wear, and it is repairable at the end of that period. The expensive shoe is cheaper, but only because it survived long enough.
If the expensive pair had fallen apart in a year, it would have cost eighty-six cents per wear. Same price tag, completely different outcome. This is why brand alone tells you nothing.
Where cost per use misleads
It rewards buying things you will use constantly and punishes buying things you use rarely, which is broadly correct but can tip into absurdity. A commercial espresso machine has a wonderful cost per use if you drink six shots a day and a terrible one if you do not.
It also ignores the ceiling. Buying the most durable option in every category means tying up real money in objects, and cash flow matters more than theoretical efficiency for most households.
And it says nothing about whether you need the item at all. A zero dollar non-purchase beats every calculation on this page.
Applying it before you buy
Estimate uses per month, then multiply by the months you expect to keep it. Be conservative: cut your estimate in half. If the item still beats the alternative at half the uses, the decision is safe.
Do this only for purchases above a threshold you set, maybe twenty-five dollars. Doing it for a bag of carrots is a waste of attention and will make you stop doing it entirely.
Write the number down. A purchase you predicted at thirty cents per use and later measured at ninety is information you can use next time.
The repair variable
Anything repairable has a lower cost per use than the price suggests, because the second and third lives are nearly free. A boot that can be resoled is a different object from one that cannot, even at the same price.
Check repairability before buying. Are there replacement parts? Can the battery be changed? Is the zip a standard size? These questions take two minutes on a product page and they change the arithmetic significantly.
The flip side is that repairability only pays if you actually repair. An unrepairable object you replace is expensive; a repairable object you replace is just as expensive.
Keeping it from becoming a spreadsheet
You do not need to track everything. Pick the three categories where you spend the most, work out the number once, and let the rest go.
Revisit twice a year. Prices move and so does your usage, and a number from two years ago is not evidence about today.
And keep the calculation rough. Two significant figures is plenty. Precision here creates an illusion of accuracy that the underlying estimates do not support.
The categories where the number is hard to estimate
Some purchases resist the calculation entirely. Gifts, medical equipment and anything bought under time pressure do not fit a formula, and forcing them to is a waste of energy.
Tools sit in a middle ground. A drill used twice a year has a terrible cost per use on paper, but the alternative is paying someone eighty dollars each time you need a shelf up. Count the avoided callout fee, not the number of holes.
Clothing for occasional events is the hardest case. A suit worn four times a year looks expensive per wear, but renting four times a year costs more than owning for a decade. Compare the two options against each other rather than against an abstract ideal.
Where the number genuinely cannot be estimated, default to the cheapest option that does the job properly. You can always upgrade later with better information, and the first purchase teaches you what you actually needed.
One final caution. Do not let a good cost per use talk you into a purchase you were not planning. The formula ranks the options in front of you. It does not tell you that you need any of them.
Pick one thing you are about to buy and work out the cost per use before you pay. Then write the figure on the receipt and keep it. In six months you will know whether your estimate was good, and that knowledge is worth more than any buying guide.