The four numbers that determine affiliate income
Affiliate income is a straightforward multiplication problem once you break it into stages: how many people see your content, what share of them click an affiliate link, what share of those clicks turn into a sale, and how much you earn per sale. Most beginners only think about the last number (commission rate) when the first two — audience size and click-through rate — usually matter more.
Click-through rate on affiliate links typically runs 1–5% for blog and content-based recommendations, higher for a dedicated 'best tools' or review page (5–10%+) and lower for a passing mention buried in unrelated content. This is why a smaller, more targeted audience often out-earns a bigger, less-engaged one — a 10,000-visitor review page with 8% CTR beats a 50,000-visitor general blog with 1% CTR.
Earnings per click (EPC) is the metric that ties it all together and the one worth tracking over time — it's the actual revenue produced per affiliate link click, and it lets you compare completely different offers (a $10 SaaS commission vs. a $200 course commission) on equal footing.
Why conversion rate varies so much by traffic type
Conversion rate — the share of clicks that become sales — swings enormously based on intent. Someone reading a detailed comparison article ('X vs. Y: which is better') is close to a buying decision and converts at 5–15%. Someone scrolling social media who clicks an affiliate link out of curiosity converts closer to 1–3%. This is the real reason SEO-driven comparison and review content tends to out-earn social traffic per visitor, even when social reaches more people.
Commission structure matters just as much as rate. A 30% commission on a $20 product ($6) can lose to a 10% commission on a $300 product ($30) — always compare commission in dollars per sale, not just the percentage advertised in the affiliate program.
Worked example
10,000 monthly visitors, a 3% click-through rate and 4% conversion rate on a $60 average order with 15% commission: that's 300 clicks, 12 sales, $9 commission per sale, and $108/month — a modest but realistic number for a smaller content site. Double the CTR to 6% (by writing more comparison-style content instead of passing mentions) and income doubles to $216/month with the exact same traffic — which is why optimizing click-through often beats chasing more visitors.