Assemble the true cost of one unit
Product cost is what the unit itself costs you: materials, manufacture or wholesale. On top of it sits the per-unit overhead that exists only when something sells - outbound shipping, packaging, marketplace fees, payment processing apportioned to a single sale - and the page adds the two before it divides anything.
Pricing from product cost alone while the platform and the carrier take their cuts out of the same price is the most common way a margin quietly disappears. A $12 unit with $3.50 of overhead is a $15.50 unit as far as any price calculation is concerned, and the table keeps the two lines separate so it is obvious which one moved the answer.
A product cost of zero stops the page instead of returning a price. The message asks for what one unit costs to make or buy, and it appears even when the overhead fields are filled in, because a percentage margin on a zero cost has nothing to stand on.
Margin is the share of the price that is profit
A target margin says what share of the sale price should be left after costs. At 40 percent the cost has to equal the other 60 percent, so the price is $15.50 divided by 0.60 - $25.83 - and the profit left per unit is $10.33. That one division is the entire calculation; everything else on the page exists to show what it did.
The same target written as a markup gives a different answer. Adding 40 percent on top of cost produces a margin of about 28.6 percent rather than 40, which is why the markup on cost is printed beside the margin even though only the margin was asked for.
The margin input is capped at 95 percent, so the divisor never falls below 0.05 and a price can always be returned. Pushing the target toward that ceiling produces very large prices for very small profit per unit, which is the arithmetic working correctly rather than a fault.
The page solves for the price
Given a unit cost and a target margin, one division fixes the price, and the table prints the route line by line: product cost, other costs per unit, total cost per unit, target margin, sale price and markup on cost. Change any field and the whole route reprints, so the price is never a number detached from the chain that produced it.
The hero repeats the same result as three statistics - markup, total cost and profit left per unit - because those are the three figures a price is usually judged by. The downloadable breakdown carries the same lines for a spreadsheet, where a pricing argument usually has to survive a second reading.
A quick sanity check reads the table from the bottom up: if the total cost line is already close to the price you had in mind, the formula is not what is wrong with the product economics, and no target margin will repair a cost structure that does not fit the market.
What the price does not mean
The returned price is not a promise that anyone will pay it. It is the price at which the margin you asked for is genuinely left over, and if the market refuses that price the honest choice is between lowering the target and changing the cost - not between two invented prices that both fail the margin test.
The page does not forecast volume, because a margin on zero sales is still zero. It also leaves sales tax and VAT out: those sit on top of the tag for an end customer, and they are not taken out of your margin here.
A margin only exists once money changes hands, which is why the note under the result calls the output arithmetic rather than a price promise. Use it to learn the floor your pricing has to clear, then test the number against the market yourself.
Where the target margin leaks after the price is set
The price the page returns assumes the costs you typed are the only ones taken out of it. Add a 15% marketplace referral fee on top and the arithmetic changes: a $25.83 price that leaves 40% on a $15.50 unit leaves 25% once the fee is deducted, because the fee comes off the sale, not off the cost. Holding the 40% margin with that fee needs $34.44 - a third more expensive, which is why a marketplace product usually needs a different margin target from a direct one.
Discounts leak the same way. Twenty percent off $25.83 is $20.66, and the margin falls to 25% on the same unit cost. That is the arithmetic reason a discount is never "just" a discount: it comes entirely out of the profit line, because the cost did not move.
Returns are the quietest leak. A 5% return rate refunded in full costs $1.29 a unit at this price, which takes the 40% margin to about 35% - and if the returned unit cannot be resold, the cost doubles. Sizing a returns allowance into "other costs per unit" is the honest way to price it; leaving it out is how a 40% plan quietly becomes a 35% year.
What none of this changes is the direction: costs fall on the unit, fees and discounts fall on the price, and the margin you want has to be defended against both if the plan is to survive contact with a marketplace.
Danfio