CPA - Cost Per Action (also called Cost Per Acquisition) - is a performance metric that measures how much a brand spends to generate a single desired user action from a campaign. It is the most commercially direct metric in digital and influencer marketing: it connects investment to outcome, making it the preferred KPI for conversion-focused campaigns.
What is Cost Per Action?
CPA is calculated by dividing total campaign spend by the number of completed desired actions:
> CPA = Total campaign spend ÷ Number of actions
The "action" is defined by the campaign objective:
- Purchase - the most common; also called Cost Per Acquisition
- Sign-up - newsletter subscription, account registration
- Download - app install, ebook download
- Lead - form submission, demo request
- Trial - free trial activation
Example: A brand spends €5,000 on an influencer campaign that drives 100 purchases. CPA = €5,000 ÷ 100 = €50 per purchase.
CPA in Influencer Marketing
Tracking CPA from influencer campaigns requires reliable attribution. The most common methods:
Unique promo codes. Each influencer receives a distinct discount code (CREATOR20). When a purchase is completed using the code, the sale is attributed to that creator. Clear, reliable, and audit-friendly.
UTM-tagged links. Unique trackable URLs assigned to each influencer. When a user clicks and subsequently converts, the conversion is attributed via Google Analytics or similar. More detailed than promo codes but dependent on link clicks.
Affiliate tracking. Influencers earn a commission per conversion, creating aligned incentives. The affiliate platform tracks CPAs automatically.
CPA as a Pricing Model
Beyond being a measurement metric, CPA can also be a payment model in influencer campaigns - particularly for affiliate or performance-based partnerships. The influencer is paid a fixed amount per conversion they drive, rather than a flat fee per post. This model:
- Aligns influencer incentives directly with brand outcomes
- Reduces upfront risk for the brand
- Can undervalue high-quality awareness content that contributes to conversions through other channels
- Is most appropriate for influencers with audiences that have demonstrable purchase intent
Benchmarking CPA
A CPA from influencer content should be benchmarked against:
- The brand's CPA from paid social advertising (Meta, TikTok)
- The brand's CPA from Google Ads
- The brand's average customer acquisition cost across all channels
If influencer CPA is competitive with or below paid social CPA, the channel is performing efficiently. Many brands find that conversion rates from influencer promo codes (indicating purchase intent) are higher than equivalent paid social traffic.
