Definition
Incremental lift (also called incrementality) is a measurement approach that determines the true causal impact of an email campaign. Instead of attributing all conversions to email (last-click attribution), incremental lift compares the conversion rate of subscribers who received the email against a randomly selected holdout group who did not receive it.
Incremental lift answers the question: "How many of these conversions would have happened anyway, even without this email?"
Incremental Lift Example
| Group | Size | Conversions | Conversion Rate |
|---|---|---|---|
| Email recipients | 10,000 | 500 | 5.0% |
| Control (no email) | 10,000 | 200 | 2.0% |
Incremental lift = 5.0% - 2.0% = 3.0% incremental conversion rate Incremental conversions = 10,000 × 3.0% = 300 additional conversions
Without lift measurement, you would attribute all 500 conversions to email. Lift measurement shows that only 300 of those 500 were truly caused by the email.
Why Incremental Lift Matters
- Accurate attribution: Last-click attribution overstates email impact because many subscribers would have converted through another channel.
- Budget justification: True incrementality data is more credible for budget requests than last-click data.
- Campaign optimisation: Identify which campaigns drive real incremental value vs those that capture conversions that would have happened anyway.
- Channel comparison: Compare the true incremental impact of email against other marketing channels.
How to Measure Incremental Lift
| Step | Action | Notes |
|---|---|---|
| 1. Randomly split audience | 90% receives email, 10% holdout | Random assignment is essential |
| 2. Send campaign to test group | Normal campaign delivery | Do not modify for the test |
| 3. Measure conversions in both groups | Same measurement window | Typically 7-14 days |
| 4. Calculate incremental lift | Test conversion rate minus control rate | Statistical significance check |
| 5. Apply learnings | Use data for optimisation and budgeting | Repeat regularly |
Average Benchmarks
| Campaign Type | Typical Incremental Lift |
|---|---|
| Promotional broadcast | 20-40% of total attributed conversions |
| Automated sequence | 40-60% of total attributed conversions |
| Newsletter | 10-30% of total attributed conversions |
| Re-engagement | 30-50% of total attributed conversions |
Incremental Lift Best Practices
- Use holdout groups regularly: Run holdout tests quarterly to validate your attribution model.
- Ensure statistical significance: Random holdout groups should be large enough (minimum 1,000 per group) to produce reliable results.
- Measure across channels: Holdout tests that suppress email entirely (no email for a period) provide the most accurate picture of total email incrementality.
- Document results: Build a library of incremental lift results by campaign type to inform future budgeting and strategy.
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Related Glossary Terms
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A/B testing in email marketing is the practice of sending two variations of an email to a small sample of your list to determine which version performs better before sending the winner to the remaining subscribers.
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Abuse Complaint
An abuse complaint is a report from a recipient who marks an email as spam, which negatively affects sender reputation and deliverability.
AI Email Summary
An AI email summary is a short, machine-generated overview of an email's key points, shown by Gmail, Outlook and Apple Mail before a recipient opens the message. It is reshaping how email marketers think about subject lines, preview text and open rates.
AI Inbox Summary
An AI inbox summary is an AI-generated digest that condenses unread email — often highlighting news, actions and senders — changing how clearly your marketing email reaches and engages subscribers.
AI Inbox
An AI inbox is an email client that uses artificial intelligence to summarise, sort, prioritise and sometimes answer emails before the human recipient reads them. It is transforming email marketing metrics and copywriting.
Frequently Asked Questions
Attributed conversions include all conversions that occurred after an email was sent. Incremental lift subtracts the conversions that would have occurred without the email. Attributed conversions overstate email impact. Incremental lift shows true causal impact.
Holdout groups should be 5-10% of the test population, with a minimum of 500-1,000 subscribers per group for statistical significance. For large lists, 10% holdout provides reliable data without sacrificing significant revenue.
Yes. For automated sequences, create a holdout group of subscribers who meet the trigger conditions but do not receive the sequence. Compare their outcomes to those who received the sequence.
Yes. If the control group converts at a higher rate than the email group, incremental lift is negative. This indicates the email campaign is actively reducing conversions — perhaps through poor timing or irrelevant content.
Run incremental lift tests quarterly for your highest-volume campaigns. Annual comprehensive lift measurement across all campaign types provides strategic data for budget allocation.