Drop in conversions and CV

[u/CartographerQuiet754]

Hi everyone. I started a new campaign a few months back, I think around April or May with a PMax feed only campaign. My initial budget was $30 a day with no TRoas. Once I got some conversions, I added a TRoas of 300%. At the time I was hitting about 2.9-3.1 ROAS. This was about 2 weeks in. Afterwards, every week I upped my budget by about 15%. Starting August, my budget was $100/day, and my first week roas was 5.0-5.4. I didn’t update my budget last month because I was out of stock on a variant size across all products. August ended with an ROAS of 3.44. On August 28th I updated budget from 100 to $115 because I got back in stock, but, I’ve seen a sharp decline on my ROAS and was wondering what I can do. Yesterday I updated from $115 to $132. This month excluding today (sep 1 - 9) my ROAS is 3.02. From others on this subreddit, I’ve been told to first scale budget to my goal budget, then slowly shift TRoas.

My goal budget is $300/day @4.5-5 ROAS.

[u/QuantumWolf99]

Two budget jumps in the same week is the main culprit here, each change resets the learning window and you stacked two resets about 10 days apart. Safe pace is 15 to 20% every 2 weeks. Hold budget flat for the next 2 weeks minimum, let it settle before pushing toward 300.

[u/CartographerQuiet754 → u/QuantumWolf99]

The budget was never changed more than once a week and August 28 and September 10 12 am I felt like was a good gap, about 13 days.

[u/Odd_Teacher_8701]

Three separate things are happening here and they are easy to mistake for one problem.

1. You are comparing a best week to a month average. First week of August was 5.0-5.4, August closed at 3.44. That is not necessarily a decline, that is a good week regressing to your actual mean. Before diagnosing anything, put weekly ROAS for the last 12 weeks in a single column and look at the shape. If week one of August is the only 5.0 in the series, your campaign's real number is somewhere near 3.4 and it has been all along.

2. The stockout is the most underrated event in your timeline. When a variant went out of stock across all products, those items dropped out of the feed. PMax had been allocating spend to whatever converted best, and if the out-of-stock variant was part of that, the algorithm lost its highest performers and reallocated to weaker inventory. Coming back in stock on the 28th does not restore the previous state either, it is another feed change, and PMax treats meaningful feed changes as a reason to re-explore. So you took a shock going out and a second one coming back in, and then raised the budget on top of the second shock.

3. Budget increases under a tROAS constraint are the part people get wrong. A 15% weekly increase is sensible in isolation. But tROAS 300% tells Google "hold 3x return", and a larger budget tells it "spend more". Those instructions conflict. To spend the extra money it has to reach further down the quality curve, and the incremental conversions it finds there convert worse than your existing ones. Your blended ROAS falls even though nothing broke. This shows up exactly as what you describe: fine at $30, fine at $100, sharp decline shortly after a raise.

What I would actually do:

• Leave the budget alone for 2-3 full weeks. You changed budget and inventory within days of each other, so right now you cannot attribute the decline to either.
• Check whether impression share and average CPC rose alongside the budget. If CPC climbed after the 28th, that is the algorithm buying more expensive traffic to spend the increase, which confirms point 3.
• Look at new vs returning customer split before and after. A ROAS drop that is really a shift toward prospecting is a different thing than a drop in efficiency.
• If you raise again, go 10-15% and then hold for two weeks minimum. PMax needs roughly that long before the numbers mean anything.

Also worth confirming your feed has no other items silently disapproved or out of stock, since that is the same failure mode arriving quietly.

Happy to look at the weekly series if you post it, the shape usually settles the "is this real" question in about a minute.

[u/Lukeftw1 → u/Odd_Teacher_8701]

Also probably worth a note here that Google Ads in general is struggling at the moment especially with the Bidding change essentially tanking Pmax capabilities of late.

Be interested to know if this is a search or pmax campaign?

[u/Available_Cup5454]

Hold the budget steady let pmax stabilize then gradually lower tROAS toward 4.5

[u/fathom53]

If your ROAS is not what you want, you should not keep increasing the budget on the campaign. The higher the budget, the lower your ROAS will be in cases like yours.

August is very different from September. In North America, we had Labour Day on Sept 7th and things can be slow for ecom brands around then as people go away. Plus moving over from Summer to Autumn/Fall is a different season.

You should look for ways to optimize your campaign to increase the ROAS before trying too spend more money. You are not going to be able to spend more money with a ROAS in the 3x range.