Cost of Goods Sold (COGS)

The COGS formula

Accounting counts cost of goods sold per period. Two routes lead to the same figure:

The first route suits a sheet with one row per item. The second works if you count stock once a month, but it quietly includes anything you binned, lost or gave away, so note write-offs as their own amount.

What goes in COGS and what doesn't

Ask of every cost: would you have paid this if you had never listed the item? If yes and it belongs to one item, it is cost of goods. If you pay it only because you sell, it is a selling cost. If you pay it whatever you buy or sell, it is overhead.

Vinted's updated Terms take effect on 8 October 2026 in Poland (5 October in Germany and France), and press reports say the Buyer Protection fee becomes the "Vinted fee". Log it by what it was, a fee you paid as a buyer, whatever it is called.

Moving a cost between lines never changes net profit on a flip. It changes gross profit, and it changes ROI, which divides by what you count as invested. Cleaning is the usual disagreement: the resale profit calculator takes it in Packaging, cleaning, other and divides ROI by Purchase cost only, while the reselling ROI calculator adds it to the base under Extra costs. ROI vs margin vs markup shows how far apart the two readings drift.

COGS and unsold stock

An item enters COGS in the month it sells, not the month you pay for it. Example: in September you spend 600 zł on stock and sell items that cost you 250 zł. September's COGS is 250 zł; the other 350 zł is still stock at cost, even though the cash is gone.

• Unsold at month end: keep its row with a blank sale date, as in the reseller inventory and profit tracker
• Returned and resellable: reverse the sale; the item goes back to stock at its original cost
• Binned, lost or given away: record the cost as a write-off so poor buys stay visible
• Cleared in a lot: its COGS is the sum of the pieces' own costs, not a new figure

When stock stops moving, how to liquidate unsold inventory covers the exits.

Worked example: splitting a lot

Lots and clothing bales arrive with one price for many pieces, so the split decides each item's cost of goods.

Split evenly at 55 zł each, the coat shows 113 zł gross profit and the shirt a 5 zł loss. Booking the whole 177 zł in September is worse: gross profit drops to 53 zł, and the jeans later look like pure profit. Decision rule: split mixed lots by expected sale price, near-identical pieces evenly, and never re-split after a sale.

Most of an item's cost of goods is fixed the moment you agree the price.

Why COGS matters for profit and tax records

• Gross profit = sales − COGS. It tells you whether you buy well, before any marketplace's fees blur it. The monthly profit and loss layout is in the reselling profit guide.
• Buying limits. A maximum buy price or ROI floor is only as honest as the cost of goods behind it.
• Tax records (Poland, general information, not tax advice). podatki.gov.pl works out income on a private item sold within six months (counted from the end of the purchase month) as revenue minus acquisition cost, plus outlays, filed on PIT-36. For unregistered activity, biznes.gov.pl describes PIT-36 on the tax scale with costs deductible. Neither page defines COGS for resellers, so ask a doradca podatkowy which of your costs count and what proof to keep. The rules are summarised in reselling in Poland without registering a business.