How to Calculate Your True Profit Per Product (Most Sellers Get This Wrong)

Most online sellers track revenue. Far fewer track profit per product — and that’s the number that decides whether your shop actually makes money. Here’s the formula, the four numbers people fudge, and how to get an honest answer in two minutes.

The formula

True net profit per unit = sell price − product cost − shipping − platform fees − payment fees − ad spend per unit.

It looks obvious. The trouble is that four of those six usually get skipped or guessed — which is how a “profitable” product quietly loses money.

The four numbers sellers get wrong

• Platform fees. Etsy takes ~6.5% plus listing fees; Amazon’s referral fee runs 8–15%. These come off the top of every sale.
• Payment processing. Roughly 2.9% + $0.30 per order — small per sale, but it compounds fast.
• Shipping you actually eat. If you offer “free” shipping, that cost is yours — subtract the real label price, not what you charged.
• Ad spend per unit. Total ad spend ÷ units sold. Spend $200 and sell 40 units, and that’s $5 off every one.

Then check your break-even ROAS

Break-even ROAS is the return on ad spend you need just to not lose money on a product. If your contribution margin is $12 on a $24 item, break-even is 2.0x — spend more per sale than that and you’re paying to lose money. Knowing this per product tells you which items can afford ads.

Do it for every product — not just the whole store

Store-level profit hides your losers behind your winners. The only way to catch a product that’s bleeding is to run each one through the same math. Our free profit calculator does it in seconds; the full Vellbrook Profit Dashboard runs your entire catalog at once and ranks them best to worst.