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In a recent blog post, we covered Google’s August 17th update: for years, Google had quietly held down bids on budget-limited campaigns, and on August 17th it stopped. Conversions from the rollout weren’t fully counted yet, so we promised you the full ROAS picture once they were.
Now there are two months of data, and the verdict is in.
Before August 17th, budget-limited campaigns beat their ROAS target by a median of about 20%. Within three weeks, that surplus was gone.
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Why budget-limited campaigns beat their ROAS target
When you set a tROAS, Google is meant to deliver roughly that ROAS. Campaigns limited by budget regularly delivered more. That extra ROAS above target is the surplus.
smec data shows how big it was:
- 55% of budget-limited campaigns beat their ROAS target, against about a third of all smart bidding campaigns.
- They beat it by more, too: a median of ~20% above target, versus ~5% for campaigns without a budget limit.
The reason: when a campaign was about to run out of budget, Google lowered its bids to stretch that budget further. Lower bids meant cheaper clicks, and cheaper clicks meant ROAS above target. On August 17th, Google stopped doing that.
One side effect is good news: budget-limited campaigns now lose impression share to budget, not rank. That makes “lost to budget” a useful diagnostic again.
So the surplus was real. but it came from Google’s bidding, not your strategy. The question was how gently it would go.
It didn’t go gently
Google said ROAS would trend toward target. It did, but not smoothly.
- The median overshoot on budget-limited campaigns dropped to roughly zero within three weeks of August 17th.
- CPCs rose on budget-limited campaigns and fell on everyone else.
- In one real account, a UK kitchen and homeware retailer, CPCs jumped 44% in a single week. Its ROAS now sits right on target.
The upside: actual ROAS now tracks target closely. Your tROAS is a more reliable lever for scaling up or holding back through peak.
But not everyone has noticed that yet.
The window most advertisers left open
Many advertisers who weren’t budget-limited raised their tROAS targets after August 17th anyway, out of nervousness. Most never lowered them again.
- If you did: it’s safe to go back.
- If your competitors did: a stricter target on their side means clicks are available on yours.
As Chris Scharmüller, our CCO, put it on our podcast Growing Ecommerce: “Actually be more aggressive now, because there’s market.”
That fixes your bids. It doesn’t answer the harder question your leadership will ask next.
If Google writes your ROAS, Google can rewrite it
For years, part of the ROAS budget-limited campaigns reported came from a Google mechanism nobody could see. Then it disappeared in three weeks, and nothing in your account changed.
Going into Q4, your CMO won’t ask about tROAS. They’ll ask where the next euro should go, and how you know.
Answering with platform-reported numbers means answering with the source that just moved under you. You’re not alone in doubting it: 91% of senior marketers say platform-reported results are overstated (Affinity Solutions, March 2026).
Luckily, that’s exactly what Mike’s next session covers:
[WEBINAR] MMM is here. Your imagination is the limit
Understanding August 17th is step one. Proving where your budget actually works is step two.
Join smec’s Head of Ecommerce Insights Mike Ryan for a 45-minute live session. You’ll leave with:
1. Why MMM, why now: stop defending budgets, start proving them, and why competing platform ROI claims can’t settle the argument.
2. How modern MMM works: a non-technical guide to Google Meridian and Meta Robyn, and what Bayesian modeling means.
3. The standard toolkit: budget allocation, ROAS saturation and adstock decay, and how to read them correctly.
4. Creative use cases: modeling profit instead of revenue, offline and store data, new vs. returning customers, promotions vs. natural seasonality.
5. From model to action: breaking Google Ads down into PMax and Demand Gen, scenario planning, and recommendations down to campaign level.
Read last year before you bid this year.
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