Understanding Amazon Ads ROI: ACoS, TACoS, and ROAS

The three numbers you need

Every Amazon ads report is built on three ratios. Once you can read them together, you can see not just whether ads "work" but whether they are making you money:

• ACoS (Advertising Cost of Sales) — ad spend ÷ ad-attributed sales. It shows how much of each advertised dollar went back into ads. Lower is better.
• ROAS (Return on Ad Spend) — ad-attributed sales ÷ ad spend. The inverse of ACoS. Higher is better.
• TACoS (Total Advertising Cost of Sales) — ad spend ÷ total sales, not just attributed sales. It reveals how much ads contribute to your overall revenue mix and how dependent your brand is on paid traffic.

Advertising only works when the inventory exists

There is a failure mode every seller hits: a campaign performs beautifully, so you scale the budget — and then the SKU stocks out. All that demand-driving spend lands on an empty listing, destroying your rank and wasting every dollar.

Advertising and inventory are two halves of one decision. Budget decisions should not be made in isolation from stock depth. The moment ad velocity outstrips what your inventory can fulfill, you are paying to damage your own listing.

How ReplenishIQ connects ads and inventory

ReplenishIQ pulls Amazon Ads performance together with inventory and finance data into a single view:

• ACoS, TACoS, and ROAS are tracked per SKU with trend signals, so efficiency changes are visible before they become a cash problem.
• Ad spend, attributed sales, and unit movement appear in one place — the same screen where you see stock depth.
• Budget guidance considers inventory readiness — an SKU running low stops being a candidate for more spend.
• Alerts fire on inefficient spend and demand surges, so you cut the losers and ride the winners — before either one hits the wrong end.