How Google Ads' Smart Bidding decides how much to bid in every auction

Marketing leads setting up a Google Ads account eventually stop typing in a manual bid and hand that decision to an algorithm. Smart Bidding is Google's umbrella term for the automated strategies that do this: Target CPA, Target ROAS, Maximize Conversions and Maximize Conversion Value. Each one resets the bid for every single auction rather than applying one fixed number across a campaign, a mechanism Google calls auction-time bidding.

The strategy chosen determines what Google optimizes for, how much conversion history it needs before it works well, and how a campaign behaves when the daily budget runs out before all eligible auctions are covered. That last point changed meaningfully in 2026, with direct consequences for any account running a tight budget against a fixed cost or return target.

What Smart Bidding actually looks at

At the moment of each auction, Smart Bidding evaluates a set of real-time signals rather than relying only on past averages. Google's own documentation lists device and operating system, physical location and location intent, time of day and day of week, remarketing list membership, the content of the search query, browser type, the specific ad and creative version, and interface language. For Shopping campaigns, the system also factors in product attributes, price competitiveness, and seasonal demand trends.

The practical effect is that the same advertiser can pay very different amounts for two searches that look identical on the surface, because the algorithm has judged one visitor more likely to convert than the other. This is the core reason Google positions Smart Bidding as a replacement for manual, rule-based bid adjustments rather than an extension of them.

Target CPA versus Maximize Conversions

Target CPA and Maximize Conversions both aim for volume, but they answer different questions. Target CPA sets bids to hit a specific average cost per conversion that the advertiser defines, which suits an account with a firm return-on-investment number in mind. Maximize Conversions has no such ceiling: it is built to spend the full daily budget while generating as many conversions as possible, and Google is explicit that this can increase spend significantly if a campaign was previously underspending its budget.

Since June 2026, Google has also simplified the naming: what used to display as "Maximize conversions with a Target CPA" now appears simply as "Target CPA," with the underlying bidding mechanics unchanged. Under Maximize Conversions, most manual bid adjustments are ignored by the system, with one exception: a device bid adjustment set to -100% still blocks bidding on that device entirely.

Target ROAS and the data it requires

Target ROAS shifts the goal from cost to value: it analyzes predicted conversion value at auction time and bids more aggressively on searches likely to produce a higher return, using reported conversion values from the advertiser's own tracking setup. Because it depends on modeling value rather than just counting conversions, Google sets minimum conversion thresholds before the strategy has enough data to work: at least 15 conversions in the past 30 days for Search and Shopping campaigns, 15 conversions with valid values across all campaigns for Display, at least 10 conversions a day (or 300 in 30 days) for App campaigns, 50 conversions in the past 35 days for Demand Gen, and 50 conversions a week for Hotel campaigns.

Target CPA has a lighter but similar data requirement. Google recommends judging performance over a 30-day window that includes at least 30 conversions before drawing conclusions. It also reports an "average target CPA" figure that is traffic-weighted and shaped by device bid adjustments, ad-group-level targets, and any changes made to the target during that period — which is why the number Google reports back can differ from the target originally entered. Daily spend under Target CPA can also run up to twice the average daily budget on higher-traffic days, evening out over the billing cycle.

Budget-constrained campaigns that once beat their own cost or return targets are now being recalibrated to hit them.

Why Google recalibrated targets in August 2026

Google's own account of the problem is that budget-constrained campaigns running Target CPA or Target ROAS could beat their stated targets — for example, a campaign set to a $10 Target CPA might actually achieve a $5 CPA. Google said this created unpredictable results whenever an advertiser then raised the budget, since performance would shift back toward the original target rather than holding at the better number the account had gotten used to seeing.

Starting August 17, 2026, Google updated its bidding systems so that budget-limited campaigns using Target CPA, Target ROAS, or Target CPC (for Demand Gen) optimize consistently toward the stated target instead of overperforming it. The change applies to Search, Shopping, Performance Max, Demand Gen and Travel campaigns managed in Google Ads or Search Ads 360, and to Demand Gen campaigns managed in Display & Video 360; App campaigns and video-focused formats are excluded. Google's own FAQ page describes the rollout as fully in effect by August 27, 2026.

Ahead of the change, Google made a Bid Target Adjustment Tool available starting July 6, 2026, letting advertisers review affected campaigns and choose to keep the existing target, reset it to match recent performance, or set a custom figure. Google was explicit that it would not adjust anyone's budgets or bid targets on its own — advertisers who took no action simply had the new, less generous bidding behavior applied against whatever target was already on file.

What to check before setting a budget

Conversion tracking has to be working correctly before turning on any Smart Bidding strategy. Google states plainly that Maximize Conversions requires conversion tracking to be set up, and Target ROAS is only as accurate as the conversion values it is fed.

Before switching to Target ROAS specifically, confirm the account clears the relevant 30-day (or 35-day, for Demand Gen) conversion minimum listed above. Accounts below that volume are better matched to Target CPA or Maximize Conversions, where the data bar is lower.

Any account that has been running Target CPA or Target ROAS on a tight budget through 2026 should treat the August recalibration as a reason to re-check its stated targets against recent actual performance, rather than assume the number set months ago still reflects what the campaign can deliver now that overperformance has been leveled out.