TACoS
Ad spend as a percentage of total revenue: the share of the whole business that goes to ads.
TACoS, total advertising cost of sales, is ad spend divided by total revenue, written as a percentage. It is the inverse view of MER: where MER asks how much revenue each ad dollar returns, TACoS asks what share of your total revenue you spend on ads.
The term comes from the Amazon world but applies to any ecommerce brand. A falling TACoS while revenue grows is the healthy signal: advertising is becoming a smaller share of a bigger number, which usually means brand demand and repeat purchases are compounding. A rising TACoS means you are leaning harder on paid to hold the same revenue. There is no universal good TACoS; like every efficiency metric it is judged against your margins and your growth goal, not an industry benchmark.
Read it as a trend, not a single day, alongside the rest of your blended picture in MER vs ROAS.
Put the number to work: the break-even ROAS calculator turns your margins into the ROAS you need, and a free Due Diligence Audit checks whether the figures you see are the ones you are getting. Back to the glossary.