Smart Bidding is the collective name for Google's five automated bid strategies: Target CPA, Target ROAS, Maximize Conversions, Maximize Conversion Value, and Enhanced CPC. Each uses machine learning to set bids at auction time based on predicted conversion probability. They differ in what they optimize toward, how much conversion data they require, and where they fail.
Understanding the mechanics of each strategy — not just the description Google gives them — determines whether Smart Bidding improves your account or creates expensive learning phases that stall performance.
Target CPA (Cost Per Acquisition) optimizes bids to achieve your desired cost per conversion. The critical requirement: at least 30 conversions in the past 30 days at the campaign level, though 50+ is where the algorithm stabilizes. Below 30 conversions, the algorithm cannot distinguish signal from noise. Accounts that enable Target CPA below this threshold frequently experience a 'false floor' — the algorithm refuses to spend because it cannot find auctions that meet the CPA target, leading to impression share collapse.
Target ROAS (Return on Ad Spend) optimizes for conversion value relative to spend. Where Target CPA treats all conversions as equal, Target ROAS accounts for the value of each conversion — important for e-commerce where different products have different margins. Threshold: 50 conversions in 30 days with conversion values assigned. Accounts that set aggressive ROAS targets (8x, 10x) without sufficient data often see low impression share — the algorithm cannot find auctions where it predicts achieving the target, so it doesn't bid.
Maximize Conversions spends your entire budget while getting as many conversions as possible with no efficiency constraint. There is no minimum conversion requirement. This is the right starting point for new campaigns that have no conversion history. The risk: Maximize Conversions will find and spend on whatever generates conversion signal, which may not align with your business goals if your conversion tracking is misconfigured.
Maximize Conversion Value spends your budget while maximizing the total value of conversions, not the count. For e-commerce, this biases the algorithm toward higher-value purchases. Like Maximize Conversions, there is no minimum conversion requirement. The distinction from Target ROAS: Maximize Conversion Value has no efficiency target — it just maximizes value within budget. Use it when you have budget to spend and want value maximization without the risk of Target ROAS restricting spend on early campaigns.
Enhanced CPC (ECPC) is a hybrid between manual and automated bidding. You set your bids manually, and Google can adjust them up or down by up to 30% based on auction-time signals. It is the least automated of the Smart Bidding strategies and has become less relevant as Maximize Conversions and Maximize Conversion Value have no minimum conversion requirements.
The learning phase and what resets it. Every Smart Bidding campaign has a learning phase lasting 7–14 days when first launched or after a significant change. The mistake most advertisers make: making changes during the learning phase. Each significant change resets it. Google's definition of significant includes: bid strategy switch, target CPA or ROAS change greater than 15–20%, budget change greater than 30%, major keyword additions or removals, and new geographic targeting. An account that makes multiple changes per week stays in perpetual learning phase.
Transitioning between strategies correctly. The recommended progression: start on Maximize Conversions (no conversion requirement, gets data) → build to 30–50 monthly conversions → switch to Target CPA or Target ROAS. When switching, avoid large target changes. If your Maximize Conversions campaigns are converting at €45 CPA, start your Target CPA at €55, not €30. Reduce targets by 10–15% increments every 2 weeks once performance is stable.
Portfolio bid strategies let you apply a single Smart Bidding strategy across multiple campaigns from a shared portfolio. For accounts where each individual campaign has insufficient conversion volume, portfolio strategies pool data across campaigns and enable Smart Bidding at the portfolio level. This is one of the most underused capabilities in Google Ads. Digital Face monitors your Smart Bidding strategy configuration, conversion volume per strategy, and learning phase status — alerting you when campaigns have insufficient conversion data for their current strategy. Free plan at digital-face.nl, no credit card required.