| Comparison | Option | Cost per use | Over 3 years | Break-even |
|---|---|---|---|---|
| Cartridge vs safety razor | Cartridge razor | $0.42 | $260 | The safety razor pulls ahead after about 3 months |
| Safety razor | $0.08 | $49 | ||
| Home clipper vs barber | Home clipper | $1.79 | $70 | The clipper pays for itself after about 2 months |
| Barber | $30.00 | $1,170 | ||
| Creatine powder vs capsules | Creatine powder | $0.18 | $191 | No crossover — the powder is cheaper from the first serving |
| Creatine capsules | $0.70 | $768 | ||
| Dumbbells vs gym membership | Adjustable dumbbells | $0.47 | $219 | The dumbbells pay for themselves after about 11 months |
| Gym membership | $1.54 | $720 |
A five-dollar razor cartridge and a fifteen-cent blade do the same job. The difference is not the price on the packet. It is what each one costs every time you pick it up, and how long you have to keep picking it up before the expensive-looking option turns out to be the cheap one.
This calculator does that conversion. Enter the price of two ways of solving the same problem, how often you use them, and how long each replacement lasts. It returns the cost per use, the total over one, three and five years, and the moment the two lines cross.
Using it
Start with one of the four examples if you just want to see how it behaves, then edit anything. The example figures are starting points, not prices — your handle may have cost you nothing because it was a gift, and your barber is probably not charging what the national average says.
The two boxes marked uses and months matter more than they look. A blade is replaced after a number of shaves. A gym fee is not — it arrives every month whether you go or not. Pick the wrong unit and the comparison is meaningless, which is why the switch exists rather than assuming everything is a consumable.
A one-off is not a replacement
The distinction between the first two boxes on each side is the part people get wrong. Cost to buy it once is for something you buy and then keep: a razor handle, a clipper, a pair of dumbbells. Cost of one replacement is for something you keep buying: blades, cartridges, a monthly fee.
Put a recurring purchase in the one-off box and the maths will flatter it badly, because it will only be counted once. Put a one-off in the replacement box and you will pay for it again and again in the arithmetic even though you never handed the money over twice.
Where the figures come from
The example numbers are market prices checked in September 2026, and two of them carry a warning that the table cannot express.
How many shaves one cartridge gives is genuinely disputed. Manufacturers claim twenty to thirty. Independent testing and the long-running shaving forums put it much lower, often between three and seven. The example uses ten, which sits between the two camps and is generous to the cartridge — if you are one of the people who replaces a blade every week, the cartridge figure roughly doubles.
What a haircut costs varies more than anything else in the table: a chain charges around $25, a big-city barber can be three times that. The comparison holds either way, because the home option wins on the second haircut regardless.
The creatine and dumbbell figures travel well. Both are bought online at broadly national prices, so the regional spread is small enough not to matter. Creatine is the cleanest comparison of the four: capsules carry the same active ingredient at roughly four times the price of the powder, and no amount of shopping around closes that gap. What creatine does and how to take it covers the dosing that the 200-servings-per-kilo assumption rests on, and monohydrate against HCL explains why the cheaper form is the one with the evidence behind it.
When the cheap option is the right one
The crossover is not an argument for always buying the dearer thing. It is a threshold, and it only pays to cross it if you expect to still be using the thing when you get there.
Somebody who shaves three times a year should buy the cartridges. Somebody who has never stuck with a gym for more than two months should not buy the dumbbells on the strength of an eleven-month payback that assumes they keep going. The tool tells you where the line is; whether you will reach it is a question about you, not about arithmetic.
The other honest caveat is that the same logic applies inside a category. A $200 set of adjustable dumbbells is not a $500 set, and the eleven-month figure moves if you buy the heavier ones. Training at home without a full rack works out what you can actually do with a limited set, and the four-day split shows the kind of schedule the three-sessions-a-week assumption is standing in for.
Grooming runs the same way. A clipper pays for itself in two haircuts, but only if you are willing to cut your own hair — which is a skill, not a purchase. Keeping a beard in shape covers the trimming routine that makes the home option workable, and growing it out in the first place is the part that no tool can speed up. If you are weighing up what to spend on supplements generally, the short list worth the money applies the same test.
What the model leaves out
Three things, and they are not small.
It counts money and nothing else. Your time is not in it. A safety razor takes longer per shave than a cartridge, and if that extra two minutes matters to you, the tool cannot know that.
Quality is not in it either. Two options can have the same cost per use and be nothing alike to use, and the dearer one may simply be better in a way that no formula captures.
And it assumes you use what you buy. The real cost per use of a gym membership is not $1.54 if you stop going in March — it is whatever you paid divided by however many times you actually went, which is the one number the calculator cannot get from you and the one most likely to change the answer.
Total spend is amortised rather than rounded. A one-off is spread across the window instead of appearing as a lump, so the five-year figure for a durable item shows the share of its life you used, not a receipt. Every assumption is editable, and the working is printed under the result so you can check it. If you want the same treatment applied to protein, the protein intake calculator does it with the ranges this site already publishes.