How Smart Bid Optimization Reduced Our Clients' CPA by 45%
Bid strategy is the engine of every Google Ads campaign. Choose the wrong one and you're either starving the algorithm of the data it needs or burning budget on low-quality conversions. Choose the right one—at the right time—and you unlock compounding improvements week over week.
Over the past 12 months, Old Fox applied a structured bid optimization framework across 40+ client accounts. The result: an average 45% reduction in CPA for accounts where the full framework was implemented. This article breaks down exactly how we do it.
The Three Bid Strategies That Actually Matter
Google offers a dozen bidding options, but in practice, nearly every campaign lives or dies by three: Target CPA, Target ROAS, and Maximize Conversions. Each serves a specific purpose at a specific stage.
Target CPA: Use It When You Have Data
Target CPA instructs Google to bid for conversions at a specific cost. It performs best when:
- The campaign has at least 50 conversions in the last 30 days
- Your conversion values are relatively uniform (lead gen, SaaS signups)
- You need cost predictability for budget planning
The most common mistake: setting Target CPA too aggressively below the historical average. The algorithm needs room to explore. We typically set it 10–15% above the current average CPA for the first two weeks, then tighten gradually as conversion volume builds.
Target ROAS: Ecommerce's Best Friend
Target ROAS is the right strategy when conversion values vary by transaction. For ecommerce brands, it allows Google to prioritize higher-value purchases over low-margin ones.
Requirements: 30+ conversions per month with accurate revenue values being passed. If your conversion tracking is passing $0 or a fixed placeholder, Target ROAS will optimize for the wrong thing.
Maximize Conversions: The Launch Strategy
New campaigns lack the conversion history smart bidding needs. Maximize Conversions (without a target) is the right starting strategy—it gets spend into the account and builds the conversion signal that Target CPA or ROAS will later use.
We typically stay on Maximize Conversions for 4–6 weeks or until we hit 50+ conversions, then transition.
The Transition Protocol
The single biggest lever in bid optimization isn't which strategy you choose—it's how you transition between them. Abrupt switches cause the algorithm to enter a learning phase, temporarily spiking CPA. Our protocol:
- Run new strategy in a separate experiment campaign (50/50 traffic split)
- Measure over a minimum of 14 days, ideally 21
- Require 20%+ improvement in CPA or ROAS before rolling out fully
- After rollout, don't change bids, budgets, or targeting for 7 days
Feeding the Algorithm: Conversion Quality Over Quantity
The most underrated factor in bid strategy performance is conversion signal quality. Google's algorithm optimizes toward whatever you tell it to—so if you're tracking add-to-carts as your main conversion goal, you're optimizing for browsers, not buyers.
Our conversion hierarchy for ecommerce:
- Primary: Purchase with revenue value
- Secondary: Checkout initiated (observation only)
- Do NOT use: Add to cart, product page views
For lead gen:
- Primary: Qualified lead (CRM integration via offline conversion import)
- Secondary: Form submission (observation only)
Importing offline conversions—even on a 7-day delay—consistently improves lead quality by giving the algorithm a clearer signal of what a good conversion actually looks like.
Portfolio Bidding: When Individual Campaign Targets Don't Work
When campaigns have fewer than 30 conversions per month, individual smart bidding strategies underperform. The solution: portfolio bid strategies. By grouping related campaigns under a single shared target, you pool conversion data across campaigns and give the algorithm enough signal to work with.
We use portfolio strategies for:
- New product launch campaigns (low conversion volume initially)
- Seasonal campaigns with short flight windows
- Brand campaigns where individual volume is low but combined signal is strong
Results: What to Expect and When
Real-world timeline based on our 40+ account implementations:
| Week | Typical Outcome |
|---|---|
| 1–2 | Learning phase — CPA may rise 15–25% temporarily |
| 3–4 | Stabilization — CPA returns to or beats baseline |
| 5–8 | Optimization phase — 20–35% CPA improvement |
| 3–6 months | Full compounding — 40–60% CPA improvement vs original baseline |
Patience is the hardest part. Advertisers who make bid changes during the learning phase reset the clock and never capture the full benefit.
The Old Fox Approach
At Old Fox, bid strategy decisions are never made in isolation. We pair smart bidding with clean conversion tracking, audience segmentation, and negative keyword hygiene to give the algorithm the cleanest possible signal. The bid strategy is a multiplier—it amplifies what's already working. If your underlying campaign structure is messy, no bid strategy will fix it.
That's why our onboarding process always starts with a full account audit before we touch bidding. The 45% CPA reduction we see in our clients isn't magic—it's the result of fixing the fundamentals first, then letting smart bidding compound on top of a clean foundation.