Custom Metrics vs. Default Metrics in A/B Testing

published on 21 July 2025

When running A/B tests, the metrics you choose can make or break your results. Default metrics, like conversion rates or click-through rates, are easy to use and great for industry comparisons. Custom metrics, however, allow you to measure specific goals tailored to your business, offering deeper insights into unique user behaviors. The choice between them depends on your objectives and the complexity of your testing needs.

Key Takeaways:

  • Default Metrics: Predefined, simple to use, ideal for quick insights and benchmarking.
  • Custom Metrics: Tailored to your goals, offering detailed insights but requiring more setup and expertise.
  • Best Approach: Combine both types. Use default metrics for a baseline and custom metrics to track business-specific outcomes.

Quick Tip: Start with default metrics if you're new to A/B testing. Gradually incorporate custom metrics as your testing strategy evolves.

3 Types of A/B Testing Metrics- Use the right ones or fail

Default Metrics: Features, Benefits, and Drawbacks

Default metrics serve as the backbone of most A/B tests, offering standardized measurements that are widely used across industries. Understanding their features, advantages, and limitations can help determine when they’re sufficient or when a more tailored approach might be necessary. Let’s explore some common default metrics, their strengths, and their challenges.

Common Default Metrics

A/B testing platforms often rely on metrics that track key user behaviors and business outcomes:

  • Conversion rate: This universal metric, with a median of 4.3%, measures the percentage of users completing a desired action, making it a reliable benchmark for performance.
  • Click-through rate (CTR): Tracks how often users click on specific elements like buttons or links, making it ideal for testing design changes or placement strategies.
  • Bounce rate: Measures the percentage of visitors who leave after viewing only one page, offering insights into the effectiveness of landing pages.
  • Revenue per user: Directly connects testing efforts to financial outcomes by calculating the average revenue generated per user during a session or specific time period.
  • Retention rate: Indicates the percentage of users who return after their initial visit. Comparing retention rates among different audience segments can reveal which groups are most likely to convert.

Benefits of Default Metrics

Default metrics are easy to use and provide immediate insights, even for teams with limited technical expertise or resources. They don’t require additional setup, making them accessible from the start.

One major advantage is consistency. Using the same metrics across multiple tests allows teams to establish a reliable framework for comparison. This consistency helps identify trends, benchmark performance, and make informed decisions based on historical data.

Another strength is their ability to provide benchmarks. For example, knowing that the median conversion rate is 4.3% makes it easier to evaluate your own performance. Additionally, their simplicity ensures that non-technical stakeholders, like marketing managers or executives, can understand and act on the results.

"Connecting your goals and project guarantees you consistently choose KPIs that make a real difference." - Chinmay Daflapurkar, Digital Marketing Associate, Arista Systems

Drawbacks of Default Metrics

While convenient, default metrics don’t always capture the full picture of user behavior. One limitation is their reliance on measurable proxies for immeasurable sentiments. For instance, users may dislike a feature, but this dissatisfaction might not immediately show up in metrics like churn rates.

Another issue is the delayed impact of user behavior. Default metrics usually focus on short-term outcomes during the testing period but may fail to account for long-term consequences. For example, dissatisfaction might lead to churn weeks or months after the test concludes.

Focusing solely on easily measurable outcomes can sometimes backfire. Optimizing for metrics like profit without considering user satisfaction or overall value can boost short-term results but harm long-term relationships.

Session-based metrics, in particular, can introduce statistical biases. As Georgi Georgiev, Managing Owner of Web Focus, explains:

"In general, most practitioners should avoid using session-based metrics due to the risk of erroneous test conclusions." - Georgi Georgiev, creator of Analytics-toolkit.com

Default metrics can also struggle to capture complex user journeys. For example, Gavin, Managing Director of Yatter, shared a case where a business selling stem cell therapy saw high traffic but frequent checkout drop-offs. While default metrics flagged the issue, session replays revealed that users needed more product information. Adding case studies and videos addressed this, leading to a 10% boost in conversions.

Finally, internal capacity constraints can limit the collection of key behavioral data. A/B testing often highlights what happened but falls short in explaining why it happened or predicting long-term outcomes. Additionally, it may not effectively identify usability problems on a website. This is where default metrics, despite their strengths, can leave gaps in understanding.

Custom Metrics: Features, Benefits, and Challenges

Custom metrics offer a way to measure what truly matters to your business by tailoring data collection to your specific goals. Unlike default metrics, which often focus on standard benchmarks like click-through rates or conversions, custom metrics are designed to track unique aspects of your business and user behavior.

How to Create Custom Metrics

Building custom metrics involves combining data points to align with your specific objectives. Most A/B testing platforms provide tools for creating these metrics, whether through their user interface or by writing custom code. The first step is to define what you want to measure. For example, if you're running a subscription service test, you might track "qualified sign-ups" by combining data like profile completion, email verification, and first purchase.

Many platforms also allow you to create formula-based metrics by using existing data fields. For instance, you could calculate "revenue per qualified visitor" by dividing total revenue by the number of visitors who spent more than two minutes on your site. For more advanced needs, tools like Google Analytics or API data feeds enable custom event tracking that captures highly specific user actions.

Segment-based metrics are another powerful option, focusing on specific user groups such as high-intent users, returning customers, or traffic sources. These metrics help you capture nuanced differences in behavior, setting the stage for more targeted and effective A/B tests.

Benefits of Custom Metrics

Custom metrics shine where standard ones fall short, offering a clearer picture of your website's performance by aligning measurements with your unique business goals. Instead of relying on generic benchmarks, you can zero in on the factors that truly drive growth.

Segment-based testing demonstrates the power of custom metrics. For example, Synchrony boosted its application submission rate by 4.5% among high-intent users by simplifying its banner's call-to-action buttons, proving the value of understanding user segments. Similarly, Build with Ferguson saw an 89% increase in purchases from recommendations. Users who engaged with these recommendations spent 13% more and bought an average of 2.4 additional items.

Custom metrics also enhance personalization strategies. By tracking specific user behaviors and preferences, you can create targeted experiences that adapt in real time to evolving user patterns. Additionally, they excel at measuring long-term value rather than just short-term wins. Metrics like a "30-day engagement score" or "customer lifetime value potential" help assess the broader impact of your changes.

Challenges of Custom Metrics

Despite their advantages, custom metrics can be complex to implement and maintain. Setting them up often requires technical expertise and careful planning. You need to clearly define custom events, ensure accurate tracking code implementation, and maintain consistency across different scenarios.

Validation is another hurdle. Custom metrics often need larger sample sizes or longer test durations to achieve statistical significance. Unlike default metrics, which are extensively tested, custom ones require careful validation to ensure they capture the right data. Even minor tracking errors can lead to skewed results.

As your business evolves, maintaining custom metrics can become a challenge. Metrics that were useful six months ago may lose relevance as your business model or user behavior changes. There's also the risk of over-complicating your analysis by creating too many metrics. This can lead to "analysis paralysis" or issues like the multiple comparisons problem, where testing numerous metrics increases the chance of false positives.

"If you aren't testing, you don't know how effective your changes are. You might have correlation but no causation." - Kyle Rush, VP of Engineering at Casper

Finally, while custom metrics provide tailored insights, they can make benchmarking against industry standards more difficult. The lack of standardization may complicate comparisons and strategic decision-making.

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Custom Metrics vs. Default Metrics: Side-by-Side Comparison

Choosing between custom and default metrics can shape the quality and relevance of your A/B testing insights. Each serves its own purpose, and understanding their differences helps you decide which is best suited for your goals.

Comparison Table: Custom vs. Default Metrics

Aspect Default Metrics Custom Metrics
Implementation Ready to use; no setup needed Requires technical setup and validation
Benchmarking Useful for industry comparisons Tailored to internal goals; benchmarking is less straightforward
Business Alignment Broad insights into general trends Matches specific business objectives
Flexibility Limited to standard measurements Customizable to fit unique needs
Learning Curve Easier for beginners Requires deeper expertise

Default metrics are great for quick, standardized insights, while custom metrics allow you to focus on goals unique to your business.

Default Metrics: Quick and Standardized Insights

Metrics like conversion rate, click-through rate, and bounce rate are the bread and butter of performance tracking. These metrics are easy to implement and offer a consistent way to compare your results with industry benchmarks. For example, when testing something simple like button colors or headline variations, default metrics give you a clear, reliable snapshot of performance.

Custom Metrics: Tailored to Unique Goals

Custom metrics, on the other hand, are designed to dig deeper. They capture specific objectives that default metrics might miss. For instance, if your business has a unique user journey or specialized conversion goals, custom metrics can provide more meaningful insights. They allow you to measure outcomes that align directly with your business model.

When to Use Each Type of Metric

Default metrics are perfect for teams new to A/B testing or for experiments that focus on common elements. They’re quick to set up and provide a solid foundation for understanding basic user behavior. Starting with these can help build confidence before diving into more complex measurements.

Custom metrics shine when you need to capture nuances that standard metrics overlook. For example, if your business focuses on revenue, you might want to track metrics like revenue per user, which integrates multiple data points. As Alex Birkett, Co-founder of Omniscient Digital, puts it:

"Revenue per user is particularly useful for testing different pricing strategies or upsell offers. It's not always feasible to directly measure revenue, especially for B2B experimentation, where you don't necessarily know the LTV of a customer for a long time".

Key Takeaway

To get the most out of your experiments, establish a clear hierarchy of metrics. Start with a primary metric to measure success, and use secondary metrics to provide a broader view of user behavior. Whether you’re looking for quick insights or diving into the specifics of your business model, understanding when to use default or custom metrics ensures your testing aligns with your goals.

Best Practices for Choosing A/B Testing Metrics

When selecting A/B testing metrics, it's crucial to align them with your business objectives. This ensures that every test generates insights you can actually use to make decisions.

Steps for Selecting Metrics

To choose the right metrics, follow these steps:

  • Define your objective: What are you trying to achieve with this test?
  • Understand your business model: Tailor your metrics to fit how your business operates.
  • Map the user journey: Pinpoint key interactions that could influence outcomes.
  • Separate primary and secondary goals: Focus on the main objective while keeping an eye on supporting data.

Your metrics need to be reliable and consistently measurable. As Chinmay Daflapurkar, Digital Marketing Associate at Arista Systems, puts it:

"Connecting your goals and project guarantees you consistently choose KPIs that make a real difference. It's important to choose metrics that can be consistently tracked and measured over time to ensure the validity of the KPIs".

The type of test you're running also impacts your metric choice. For instance, when Demand Curve worked with Segment to test chatbots, they focused on the free trial conversion rate. This made sense because Intercom research showed that website visitors are "82% more likely to convert to customers if they've chatted with you first".

A good metric has two essential traits: it should clearly indicate progress and be resistant to manipulation. Your primary metric should measure the core goal of the test, while secondary metrics provide additional context to understand the broader impact.

Combining Default and Custom Metrics

The most effective A/B testing strategies combine default metrics with custom ones.

  • Default metrics: These include conversion rate, click-through rate, and bounce rate. They're great for benchmarking and are easy to set up across different tests. If you're new to A/B testing, these metrics are a good starting point.
  • Custom metrics: These focus on specific goals unique to your business. For example, if you're testing a mobile app feature, you might track user behavior patterns that standard metrics like signup rates wouldn't capture.

To get a full picture, combine quantitative data (the "what") with qualitative feedback (the "why"). Numbers tell the story of user behavior, but qualitative insights explain the reasoning behind those actions. This dual approach helps prevent decisions based on incomplete information.

It's also important to monitor both primary and guardrail metrics. While primary metrics measure your main objectives, guardrail metrics help you spot unintended side effects that might not be immediately obvious.

Finding the Right Analytics Tools

Once you've identified your metrics, the next step is choosing tools that can track them effectively. Your requirements - whether basic or complex - should guide your selection process.

  • Evaluate your needs: If your focus is on default metrics, look for tools that handle standard measurements well. For more advanced tracking, choose platforms that offer customization, even if they come with a steeper learning curve.
  • Quantitative and qualitative analysis: Opt for tools that support both. Quantitative tools show how many users responded to a change, while qualitative tools explain why they acted that way.
  • Integration with your tech stack: Your metrics should integrate smoothly with your existing analytics tools to provide a complete view of user behavior and business outcomes.

The Marketing Analytics Tools Directory (https://topanalyticstools.com) is a helpful resource for comparing A/B testing platforms. It categorizes tools by their capabilities, making it easier to find options that meet your needs, whether you're looking for straightforward metrics or advanced customization.

Finally, prioritize security and compliance. If your business handles sensitive user data or operates in a regulated industry, ensure the platform meets your data protection requirements. Before committing, take advantage of trial periods to test the tool's capabilities with your actual data and use cases. This hands-on approach can reveal whether the platform truly meets your needs.

Conclusion

Deciding between custom and default metrics comes down to how well they align with your business goals. Default metrics - like conversion rates, click-through rates, and bounce rates - are great for benchmarking performance. On the other hand, custom metrics help you focus on specific goals unique to your organization. As we’ve explored, aligning these metrics with your objectives can turn A/B testing into a powerful tool for driving growth. It also ensures you measure success more accurately and track progress effectively.

Real-world examples highlight the value of linking metrics to business goals. Take ASOS, for instance: they saw a 25% jump in their net promoter score within just six months after rolling out a real-time feedback system to gauge customer sentiment. Similarly, Starbucks used feedback from over 4 million customers to achieve a 15% rise in customer satisfaction and a 30% boost in repeat visits within half a year.

Key Points Summary

  • Default metrics work well for industry comparisons, compliance checks, and adhering to standard benchmarks.
  • Custom metrics provide tailored insights that align with your specific goals but may be harder to benchmark.
  • Combining both types is often the most effective strategy. Use default metrics for baseline comparisons and custom metrics to measure outcomes that directly impact your business. Keep in mind, only about one in seven A/B tests results in a clear win.

Finding Tools for Advanced Metric Tracking

Balancing default and custom metrics requires the right tools. The Marketing Analytics Tools Directory is a handy resource for exploring A/B testing platforms and analytics tools. It categorizes solutions based on their capabilities, such as support for standard metrics and advanced customizations. Whether you need basic conversion tracking or robust custom metric features, the directory can guide you toward tools that meet your needs for real-time analytics and campaign performance tracking.

Look for platforms that combine quantitative analysis with qualitative feedback. This dual approach helps you understand not only what users are doing but also why they’re doing it.

FAQs

When should I use custom metrics instead of default metrics in A/B testing?

Default metrics work well for tracking common performance indicators like conversion rates, click-through rates, and bounce rates. They're particularly handy when you need quick, standardized insights or want to compare data across several campaigns.

On the flip side, custom metrics are ideal for monitoring goals that are unique to your business. For instance, if you're evaluating engagement with a specific feature, revenue per user ($), or other tailored behaviors, custom metrics can offer deeper insights that align closely with your objectives. By tailoring your metrics to match your business goals, you can make smarter, data-driven decisions that directly influence your strategy.

What challenges can arise when using custom metrics in A/B testing, and how can they be resolved?

Using custom metrics in A/B testing can be tricky. You might need larger sample sizes, face challenges in defining clear hypotheses, or struggle to pick the right variables to test. On top of that, common statistical mistakes can creep in, and some A/B testing tools might not fully support advanced custom metrics.

To tackle these challenges, start with solid preparation. Make sure your custom metrics are closely tied to your business goals and validate them before running the test. Choose A/B testing tools that allow for the level of customization you need. And don’t forget to involve stakeholders early on - this helps ensure everyone is on the same page and supports the metrics you’re testing.

How can combining default and custom metrics enhance insights in A/B testing?

Combining default metrics with custom metrics in A/B testing can give you a more complete picture of user behavior. Default metrics, like clicks, conversions, or bounce rates, provide a standard snapshot of performance. They act as a baseline, helping you understand general engagement trends.

Custom metrics, however, focus on actions that matter specifically to your business. For example, you might track how often users finish a multi-step process or interact with a certain feature. These tailored measurements let you zero in on the behaviors that align with your goals.

Using both types of metrics together allows you to dig deeper. You’ll not only get a broad sense of how your tests are performing but also gain insights into the specific actions that contribute to your key outcomes.

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