True COGS Calculator

How to calculate true COGS for ecommerce

The true COGS formula is simple addition — the hard part is remembering every line. Start with the obvious two: product cost per unit (your supplier invoice divided by units) and inbound freight per unit (the shipping bill on your last purchase order divided by units received). That pair is what most sellers call COGS, and it is where the undercounting starts.

Then add the four costs that scale with every sale: marketplace or platform fees as a percentage of the selling price, payment processing (a percentage plus a fixed fee per order), advertising spend divided by units sold, and a return-rate allowance — if 4% of orders come back, every sale carries 4% of the selling price as expected refund cost. Finally add packaging: boxes, mailers, tissue, inserts and tape are real money per unit.

Written out: true COGS = unit cost + inbound freight + platform fees + payment fees + ad spend per unit + (return rate × price) + packaging. The calculator above runs this exact formula — the same one documented on our methodology page.

Why true COGS beats “naive COGS” for every pricing decision

Say you sell a candle for $34. The supplier charges $9.50 and freight works out to $1.40, so your spreadsheet says COGS is $10.90 — a comfortable 68% margin. Now run the true COGS calculation: a 9.5% platform fee is $3.23, payment processing at 2.9% + $0.30 is $1.29, ads average $3.00 per unit sold, a 4% return rate reserves $1.36, and packaging adds $0.80. Your true COGS is $20.58 — nearly double the naive number — and the real margin is 39%, not 68%.

That gap is exactly why stores “doing great on revenue” run out of cash. Every decision that touches unit economics — pricing, discounts, free-shipping thresholds, which SKUs to reorder and which to kill — should start from true COGS, not the supplier invoice.

Where to find each input (without an accountant)

You do not need clean books to use this calculator — you need six numbers you can pull in ten minutes.

• Product cost per unit: last purchase order total ÷ units ordered.
• Inbound freight per unit: the freight/duty line on that PO ÷ units received.
• Platform fee %: your marketplace’s transaction + listing fees as a share of price — see our Etsy and TikTok Shop calculators for current published rates.
• Payment processing: most processors publish a rate like 2.9% + $0.30 per order.
• Ad spend per unit: last month’s total ad spend ÷ units sold that month (yes, include the bad campaigns).
• Return rate: refunded orders ÷ total orders over the last 90 days.

Worked example: apparel brand at $42

A small clothing brand sells a tee at $42. Unit cost is $11, freight $1.10, platform fees 8%, payment 2.9% + $0.30, ads $4.50 per unit, returns 8% (apparel runs high), packaging $0.95. True COGS: 11 + 1.10 + 3.36 + 1.52 + 4.50 + 3.36 + 0.95 = $25.79 — a 38.6% true margin. The naive calculation said $12.10 and 71%. If this brand had set its sale-price floor using naive COGS, a “30% off” promo at $29.40 would net just $3.61 per tee before fixed costs.

Run your own numbers in the calculator, then feed the resulting margin into our break-even calculator to see how many orders your fixed costs require, and into the ROAS calculator to get your real break-even ROAS.

From true COGS to restock decisions

True COGS tells you which SKUs deserve reorders; sales speed and lead time tell you when. Once you know a SKU is genuinely profitable, the next questions are inventory questions: what stock level should trigger a purchase order (reorder point), how much buffer covers supplier delays (safety stock), and — the one that actually prevents stockouts — the last calendar day you can place that PO (latest order date). ShelfOwl’s calculators answer each one, free.

Managing dozens of SKUs in a spreadsheet? The paid ShelfOwl forecaster takes one CSV of sales and stock levels and returns the latest order date for every SKU at once — join the waitlist below.