The proportion of affiliate program conversions attributable to customers who have no prior purchase history with the brand — buyers making their first-ever purchase. Calculation: (affiliate conversions from first-time buyers) / (total affiliate conversions) × 100. Benchmark: 50-70% new customer rate indicates affiliate is driving genuine acquisition; below 40% suggests affiliate is primarily re-engaging existing customers (lower incrementality — these customers would likely have repurchased anyway); above 80% indicates affiliate is reaching new audiences with no prior brand exposure (very high incrementality). Why it matters for ROI measurement: affiliate commission paid on existing customer re-purchases is lower-incrementality spend — the customer was likely to have repurchased through direct channels without affiliate influence; commission paid on new customer acquisition is higher-incrementality because the publisher genuinely introduced a new buyer; programs with high new customer percentage demonstrate stronger program ROI and brand value creation. Tracking requirement: requires integration between affiliate network conversion data and brand customer database to identify first-time vs. returning buyers at the point of conversion.
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