Google Ads: should add-to-cart be a primary conversion or secondary?

A client's e-commerce account had purchase, add to cart and begin checkout all set as primary, and Smart Bidding drifted toward cheap add-to-carts. Spend climbed while purchases stayed flat. My view is that only the purchase should be primary. Keep the other two as secondary so they still show in reporting but the bidder ignores them.

The counterargument is that micro-conversions help the algorithm learn faster on low-volume accounts, and that's fair if purchases are very rare. But with a few dozen sales a month, the add-to-cart signal is noisy and pulls bids toward browsers instead of buyers. How are others setting this up when purchase volume is low?

Demoting add-to-cart doesn't fix the drift by itself. The drift happened because all three actions counted as equal conversions with no values, so a cheap add-to-cart looked as good as a sale. Making purchase the only primary action removes that problem, but it also leaves the bidder with far fewer signals. With a few dozen sales a month, Target ROAS or Maximize Conversions can get unstable instead of sharper.

I'd keep add-to-cart primary with a small value and set purchase to a much higher one. The bidder still gets volume, but an add-to-cart is worth a fraction of a sale. The pure secondary setup makes more sense once purchases are enough for the bidder to learn from on their own. Below that it depends on volume, so check purchases per campaign before deciding.

Priya, the value math is where I'd push. A small add-to-cart value only helps if it's small relative to how often the action happens. Say add-to-cart converts at 8% of clicks and purchase at 1.5%, and you set ATC to $5 and purchase to $80. Per click, ATC brings in about $0.40 and purchase about $1.20, so add-to-cart still makes up roughly a quarter of the value the bidder sees. On a Target ROAS strategy that still pulls bids toward browsers, just more gently than before.

So before you pick a value, work out what share of total conversion value would come from add-to-cart. If it's more than a small slice, the value is still too high, and the cleaner option is purchase-only for bidding, with the other actions kept as secondary for reporting. Your volume point still stands, though. With only a few dozen sales, a purchase-only bidder can get unstable, and that's the real case for a tiny ATC value.

What's your add-to-cart rate versus purchase rate on those campaigns?

The 25% holds at those rates, but ATC and purchase rates vary a lot by campaign, so run the split per campaign instead of across the whole account. Also keep an eye on the count ratio. At 8% versus 1.5%, the bidder sees roughly five add-to-carts for every sale, so if your order values swing widely, even a small ATC value can matter more than it looks.

It depends on the bidding strategy, because values only matter under Target ROAS or Maximize Conversion Value. On plain Maximize Conversions the bidder ignores them and counts every add-to-cart as a full conversion, so no ATC value will fix the drift there.

Agreed, and on Max Conversions the only real lever is which actions sit in the campaign's conversion goals. The count setting on each action is the one people miss. If add-to-cart is set to "Every," a single shopper who adds three items or reloads the cart can log several conversions, so the signal is inflated before value even comes into it. Set it to "One" per click or session and you keep the signal without letting one browser dominate it. After that, decide at campaign level whether add-to-cart belongs in the goal set at all.