Definition
Impression share lost (budget) is the share of impressions you missed because your budget was insufficient.
Example
If eligible impressions are 100,000 and you miss 20,000 due to budget, loss (budget) is 20%.
How to use it
- Increase budget only when marginal ROAS/profit supports it.
- If you are budget-limited, prioritize high-intent segments first.
- Track alongside impression share lost (rank) to separate budget vs quality issues.
Common mistakes
- Raising budget without confirming incremental returns.
- Ignoring auction volatility and seasonality when interpreting loss.
Why this matters
This term matters because it affects how you interpret performance and make budget decisions. If you use inconsistent definitions or windows, ROAS/CPA can look "better" while profit gets worse.
Practical checklist
- Write a 1-line definition for "Impression Share Lost (Budget)" that your team will use consistently.
- Keep the time window consistent (weekly/monthly/quarterly) when comparing trends.
- Segment results (channel/plan/cohort) before drawing big conclusions from blended averages.
- Sanity-check with a related calculator from the same category on MetricKit.
- Read the related guide (e.g., Marginal ROAS: how to scale ads with diminishing returns) for context and common pitfalls.
Where to use this on MetricKit
Calculators
- A/B Test Sample Size Calculator: Estimate sample size per variant for a conversion rate A/B test given baseline CVR, MDE, significance, and power.
- CPL to CAC Calculator: Convert cost per lead (CPL) into CAC using lead-to-customer rate (and compute targets).
- Break-even CVR Calculator: Compute the CVR required to break even (and hit a target) given CPM, CTR, AOV, and contribution margin.
- Click-through Conversion Rate Calculator: Calculate click-through conversion rate (click-to-conversion CVR) and estimate required clicks for target conversions.
- ROAS Calculator: Calculate Return on Ad Spend (ROAS) and estimate contribution profit after ad spend.
Guides
- Marginal ROAS: how to scale ads with diminishing returns: A practical guide to marginal ROAS: why average ROAS misleads at scale, how diminishing returns work, and how to pick a profit-maximizing spend level.