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CarParts.com Drives Incremental Revenue with Fospha’s Always-On Measurement
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CarParts.com has been a pioneer in ecommerce since launching its website in 1999. As the marketing landscape evolved - more platforms, more complexity, more privacy changes - so too did their need for a modern approach to measurement.
The Challenge
Before working with Fospha, CarParts.com relied heavily on Last Click attribution - giving disproportionate credit to lower-funnel, conversion-focused activity. This skew made it difficult to fairly assess the true value of upper-funnel investment, limiting their ability to scale and leaving growth on the table.
The team also saw growing misalignment between what platform reporting and GA4 were telling them. With no consistent, trusted source of truth, they lacked the confidence to invest in newer or higher-funnel channels.
This is a common problem across ecommerce: performance is over-attributed to channels designed to convert demand, while under-recognizing those that create it.
The Solution
CarParts.com onboarded with Fospha in January 2025. From day one, they had access to two years of modeled performance data, giving them a long-range view of how every channel contributed to growth. Fospha’s modeling also fully integrated with their custom ecommerce platform - something no other provider had been able to do.
At the core of Fospha is a Bayesian MMM, built to model the cross-channel impact of each marketing input on revenue - across every stage of the funnel. It measures not just what drives clicks or conversions, but the unseen value of impressions—the brand activity that drives future demand across all destinations, including Amazon and TikTok Shop.
Using Beam, Fospha’s forecasting tool, CarParts.com identified a significant opportunity in Meta’s Advantage+ campaigns. Saturation curves revealed they could scale investment by 50% and still beat their paid media ROAS target by 128%, a clear signal that Meta had incremental headroom and was underutilized.
To validate this, the team launched a Meta Conversion Lift Study (CLS) from May to June 2025. The results confirmed what Fospha had already shown: Meta was driving strong incremental returns and reaching net-new audiences efficiently.
The Results
Armed with confidence from both Fospha’s daily insights and the CLS findings, CarParts.com scaled Meta investment by over 200% YoY in June 2025.
Fospha recommended a single-cell, account-wide CLS due to the model identifying that all Meta segments were exceeding efficiency targets - highlighting the breadth of opportunity.
This reallocation drove measurable gains:
- Meta became the most efficient digital channel, delivering the highest ROAS
- 68% of Meta conversions came from new customers, helping CarParts reach fresh audiences
CarParts.com also began generating a greater number of new customer conversions YoY, indicating healthy expansion of their customer base.
This validated the team’s hypothesis: Meta aligned with their audience and was their most incremental channel - but they needed the right mix of measurement tools to prove it.
The Bottom Line
CarParts.com achieved profitable growth by significantly reducing their reliance on last-click attribution and redistributing budget toward under-valued, higher-return channels.
Fospha didn’t replace experiments - it made them work harder. By operationalizing incrementality through always-on, full-funnel measurement, CarParts.com scaled smarter and faster.
Their success showcases the power of triangulating measurement approaches. Fospha delivered a continuous stream of decision-ready insights, while experiments validated those insights and unlocked even more budget with confidence.
Measurement isn’t just about reporting - it’s about multiplying growth. With Fospha, CarParts.com found the strategy, speed, and science to do just that.
