Break-even is spend divided by profit per unit
Profit per unit is the selling price multiplied by the margin you enter, and break-even is the ad spend divided by that figure. At $39.99 with a 30% margin a single sale clears $12.00, so a $500 campaign needs 41.7 sales before the spend is earned back.
The hero rounds that up to 42, because a shop sells whole units and 41 would leave part of the spend unrecovered. The exact fractional figure stays in the table, so the rounding is visible instead of sitting hidden behind the result.
A price of zero stops the page rather than returning units, since there is nothing to count sales against, and a spend or a margin of zero gets its own message: a break-even needs money to spend and a margin to earn it back with.
ROAS gets a break-even floor, not a target
The ROAS floor falls out of the same division. Sales at break-even divided by the spend is the same thing as one divided by the margin, so a 30% margin needs 3.33x and a 15% margin needs 6.67x whatever the budget is. Spend cancels out: doubling the campaign doubles the sales needed and leaves the required return exactly where it was.
That is why the number is a floor and not a target. It says what a campaign must return to give your money back, not what it will return, and the page prints it beside the units so the two readings of the same arithmetic can be checked against each other.
The margin field stops at 90%, which puts the floor at 1.11x: a product that is almost all profit needs barely more than its own spend back, and no setting can produce a campaign that pays for itself on less than a dollar.
Margin is the input you control most
The margin is your number, not a rate the page knows. The 30% default is a placeholder, and if you normally sell on discount it overstates what each sale clears: a 20% discount on a product whose cost is fixed can pull a 30% margin down to roughly 12.5%, and the units needed then roughly triple.
Because every line on the page is a multiplication or division of the same three inputs, that sensitivity is worth seeing before a budget is committed. The table prints profit per unit, break-even units, sales at break-even and the ROAS floor, and one change to the margin moves all four at once.
The honest way to choose the margin is from a statement, after discounts and platform fees, rather than from the price list. A hopeful margin makes advertising look cheap and quietly raises the volume the campaign has to deliver.
What gets left out, on purpose
There is no traffic, no conversion rate and no cost-per-click anywhere on the page. Those are forecasts, and a break-even that invented them would look more helpful while being less true, so the page prints the arithmetic and leaves the traffic question to the platform reporting you can actually observe.
The list under the result states what the number is not: not a traffic target, and not a promise that every sale clears the same margin, since a bundle, a coupon or a return each change the real per-unit profit. It also answers when the spend is earned back, not whether the campaign was worth running - that second question sits next to the profit that stays behind, which the ROAS calculator prices.
Read the result as a conditional: if these units sell, here is where the spend is repaid. Predicting whether they will is the market's job, and pretending otherwise is how a budget gets approved on a number that was never a forecast.
Break-even is a floor, not a profit
The units the page prints are the point where the campaign has earned its spend back — nothing more. At the defaults, $500 of ad spend against $12.00 of profit per unit needs 42 units, which is $1,680 of sales and a 3.36x return on ad spend. That is the number where the ad stops costing you money, not the number where the month is good: the 43rd unit is the first one that leaves something behind, and a campaign that lands exactly on 42 has bought nothing but the right to keep going.
Three things move the floor after you have read it. A return rate of 5% raises the effective units by about 5%, because a returned unit takes its profit back with it. A discount is worse than it looks: 20% off a 30% margin leaves 12.5% margin, so the same $500 now needs 100 units rather than 42. And repeat purchases do not help this month at all — they arrive after the campaign has already been judged. The page prices one campaign against one margin; a real account is a sequence of them, and the floor has to be cleared every time.
Danfio