Smart Bidding Strategies Explained: When to Use Each One
Google Ads Smart Bidding uses machine learning to set bids automatically at auction time, accounting for signals like device, location, time of day, audience, and dozens of other factors that manual bidding simply cannot process. But choosing the right Smart Bidding strategy — and setting it up correctly — is the difference between scalable growth and expensive mistakes. This guide explains every Smart Bidding strategy, when to use each one, and the common pitfalls that trip up advertisers.
What Is Smart Bidding?
Smart Bidding is a subset of Google's automated bidding that specifically optimises for conversions or conversion value. Unlike simple automated strategies like Maximise Clicks, Smart Bidding uses real-time auction signals to predict the likelihood of a conversion and sets bids accordingly.
The available Smart Bidding strategies in 2026 are:
- Target CPA (Target Cost Per Acquisition)
- Target ROAS (Target Return On Ad Spend)
- Maximise Conversions
- Maximise Conversion Value
Each serves a different objective, and using the wrong one for your situation can waste significant budget.
Target CPA: Controlling Your Cost Per Lead
Target CPA tells Google to get as many conversions as possible at or below your specified cost per acquisition. The algorithm adjusts bids for each auction based on the predicted conversion probability.
When to Use Target CPA
- Lead generation campaigns where each lead has roughly equal value
- Service businesses with a known cost-per-lead threshold
- Campaigns with at least 30 conversions in the past 30 days
Setting Your Target
Start with a target CPA 10-20% above your current average CPA. This gives the algorithm room to learn without overspending. Gradually reduce the target as the algorithm stabilises, but never drop it by more than 15-20% at a time — aggressive changes cause the algorithm to reset its learning.
Target ROAS: Optimising for Revenue
Target ROAS tells Google to maximise conversion value while maintaining your specified return on ad spend. If you set a 500% target ROAS, Google aims to generate £5 in revenue for every £1 spent.
When to Use Target ROAS
- E-commerce campaigns where conversion values vary (different product prices)
- Campaigns with at least 50 conversions in the past 30 days (higher data requirements than Target CPA)
- Accounts with accurate conversion value tracking in place
Setting Your Target
Calculate your minimum viable ROAS based on your product margins and business costs. If your average margin is 40%, you need at least a 250% ROAS to break even — then add your desired profit margin on top. Start with a target 10% below your current ROAS to avoid restricting volume.
Maximise Conversions: Volume First
Maximise Conversions tells Google to get as many conversions as possible within your daily budget, without a specific cost target. The algorithm will spend your full budget every day.
When to Use Maximise Conversions
- New campaigns that need to build conversion history
- Campaigns where hitting a budget ceiling matters more than efficiency
- Promotional periods where you want maximum volume regardless of cost
Important Considerations
Without a CPA target, Maximise Conversions will spend your entire budget — even if CPAs rise dramatically. Always monitor cost per conversion closely and be prepared to add a target CPA once you have enough data.
This strategy pairs well with sound campaign structure that ensures budget flows to the right keywords and ad groups.
Maximise Conversion Value: Revenue Focus Without a Target
Similar to Maximise Conversions but optimises for total conversion value rather than conversion count. Google prioritises high-value conversions over low-value ones within your budget.
When to Use Maximise Conversion Value
- E-commerce campaigns with variable order values
- New campaigns building toward Target ROAS
- Accounts where revenue growth is the priority over efficiency
Portfolio Bidding Strategies
Portfolio bidding applies a single Smart Bidding strategy across multiple campaigns, allowing the algorithm to optimise budget and bids across the entire portfolio. This is particularly powerful when individual campaigns do not have enough conversion data to optimise effectively on their own.
When Portfolio Bidding Excels
- Multiple campaigns targeting similar audiences or products
- Campaigns with individually low conversion volumes that together meet Smart Bidding thresholds
- Situations where you want a single CPA or ROAS target across related campaigns
Portfolio Bidding Setup
Create portfolio strategies in Google Ads under Tools and Settings, then Bid Strategies. Apply the portfolio strategy to the relevant campaigns. Set shared budgets if appropriate to allow Google to shift spend between campaigns based on opportunity.
Data Requirements and the Learning Period
Every Smart Bidding strategy goes through a learning period when first applied or after significant changes. During this period, performance may fluctuate as the algorithm tests different bid levels.
Minimum Data Thresholds
- Target CPA / Maximise Conversions: 30 conversions in the past 30 days (recommended)
- Target ROAS / Maximise Conversion Value: 50 conversions in the past 30 days (recommended)
- Portfolio strategies: Combined volume across all campaigns in the portfolio
You can use Smart Bidding with less data, but expect higher variance and longer learning periods. For accounts with limited data, see our guide on industry benchmarks to set realistic initial targets.
Common Smart Bidding Mistakes
Changing Targets Too Aggressively
Dropping your Target CPA by 30% overnight forces the algorithm to relearn, causing performance dips. Make gradual adjustments of 10-15% and allow 1-2 weeks between changes.
Not Enough Conversion Data
Smart Bidding with fewer than 15 conversions per month is unreliable. Consider using micro-conversions (like add-to-cart) as secondary signals, or consolidate campaigns to increase data density.
Ignoring Conversion Quality
Smart Bidding optimises for whatever you tell it to optimise for. If your conversion tracking counts low-quality form submissions alongside genuine leads, the algorithm will happily deliver more low-quality submissions. Ensure your conversion tracking reflects real business value.
Choosing the Right Strategy: A Decision Framework
Use this framework to select the right Smart Bidding strategy for your situation:
- New campaign, no data? Start with Maximise Conversions, then transition to Target CPA after 30+ conversions
- Lead generation with fixed lead values? Target CPA
- E-commerce with variable order values? Target ROAS or Maximise Conversion Value
- Multiple low-volume campaigns? Portfolio bidding with a shared target
- Scaling phase, budget is the constraint? Maximise Conversions or Maximise Conversion Value
If you run Performance Max campaigns, Smart Bidding is mandatory. Understanding these strategies helps you set appropriate targets for PMax, which uses the same underlying algorithms.
Frequently Asked Questions
Can I switch between Smart Bidding strategies?
Yes, but every switch triggers a new learning period. Avoid switching strategies frequently. If you need to change, time it during a low-impact period and allow 2-3 weeks for the new strategy to stabilise before evaluating results.
Does Smart Bidding work for small budgets?
It can, but the learning period is longer and performance variance is higher with small budgets and low conversion volumes. If you spend less than £500/month on a campaign, consider using Enhanced CPC (a lighter form of automation) or consolidating campaigns to increase data density. Portfolio bidding across small campaigns can also help.
Should I use Target CPA or Target ROAS?
Use Target CPA when all conversions have roughly the same value (e.g., lead generation). Use Target ROAS when conversion values vary significantly (e.g., e-commerce with products at different price points). If you are unsure, start with Target CPA — it is simpler and requires less data to work effectively.
What happens if I set my targets too aggressively?
Setting targets that are too aggressive (very low CPA or very high ROAS) causes Google to significantly reduce your ad spend because it cannot find enough auction opportunities that meet your target. Your impression share will drop, and you will lose volume. Set targets that are realistic based on historical data and adjust gradually.
Smart Bidding is a powerful tool, but it requires thoughtful setup and ongoing management. If you want help selecting and optimising the right bidding strategy for your campaigns, get in touch with Spires Digital or book a free strategy call via Calendly — we will analyse your account data and recommend the approach that drives the best results.