How it works
Give each option a price and how many uses it lasts before it wears out or you'd stop using it. If you'll sell it when you're done, or it costs something every use (pods, fuel, cleaning), add that under "More costs".
The calculator compares the options over the same number of uses: the uses you need, or, if you leave that blank, the longest-lasting option's life. Each time an option runs out of uses, it counts buying it again at the same price, which is why a cheap option's line jumps. That's the Boots theory from Terry Pratchett's Men at Arms, as arithmetic.
Cost per use is the total divided by the uses. The chart draws it for every count from the first use, and marks the use from which the cheapest option over your count stays cheapest: where the pricier one pays off.
Totals are exact; per-use figures are rounded to the cent. The answer is only as good as your guess of how long each lasts, so try a lower guess and watch the pay-off point move. Nothing you type leaves this device unless you copy the link.
Questions people ask
- How do you work out cost per use?
- Take what it costs you, minus anything you'll get back by selling it, plus any cost each time you use it, and divide by the number of uses. A $180 pair of boots worn 450 times is $0.40 a wear. To compare two options fairly, count them over the same number of uses, buying the shorter-lived one again when it wears out.
- When is the more expensive one actually cheaper?
- When the cheaper one has to be bought again, or costs more each use, often enough to overtake it. With $180 boots that last 450 wears against $40 boots that last 80, the cheap pair has cost more from the 321st wear (five pairs, $200), and by 450 wears it's six pairs and $240.
- Can I compare renting with buying?
- Yes: enter the rental as an option that costs the rental price and lasts 1 use. A $400 machine against renting one at $35 a time pays off at the 12th use, when renting reaches $420.
- What is the Boots theory?
- Terry Pratchett's observation in Men at Arms (1993): good boots at fifty dollars last years, while ten-dollar boots wear out, so over ten years the poorer man "might have paid out a hundred dollars on boots, twice as much as the man who could afford fifty dollars up front". It holds only if the good pair really lasts, which is the number this calculator asks for.
- What's a good cost per wear?
- There's no standard figure; Lounge's guide says "There is no definitive answer to what constitutes a 'good' or 'bad' cost per wear figure". Comparing options over the same uses is more useful than any threshold, and the total matters too: as Primer Magazine puts it, a $1,200 coat at $2 a wear "is still $1,200 you don't have anymore".