Formula
TACoS = ad spend ÷ total retail sales × 100
Worked example
Suppose a product records $10,000 in total retail sales and $2,000 in ad spend over a matched period. TACoS is 20%. If the Ads report separately attributes $8,000 of sales to advertising, ACoS is 25%. The two percentages answer different questions because their denominators differ.
If total sales rise to $12,000 while spend remains $2,000, TACoS falls to about 16.7%. That arithmetic alone does not explain why sales rose. Price changes, availability, seasonality and demand may all matter. It also does not prove that the extra sales were generated by earlier advertising.
Why it matters for profit
TACoS shows how much of the total sales base advertising consumes, but it leaves product costs out. A 20% ratio could leave contribution on a product with a 40% pre-ad margin and exhaust it on one with a 20% margin. Review product-level economics before treating a falling ratio as evidence of better profit.
Match marketplaces, currencies, products, refunds and reporting dates before using the ratio. Ads and retail reports may recognize sales differently. Subtracting one report’s attributed sales from another report’s total sales does not reveal exact organic sales. Keep that reporting limitation separate from the simple division.