PBN IFR is the ratio of inbound links a PBN domain receives from external sources versus the footprint it creates by linking out to target sites. If a PBN site has 50 referring domains pointing to it but sends links to 20 money sites, its IFR is 2.5:1, which looks healthier than a site with 5 inbound links supporting 30 outbound links (0.17:1). The concept exists because Google's algorithms evaluate whether a site exists to serve users or solely to pass PageRank. Legitimate blogs naturally accumulate inbound links from citations, social shares, and organic discovery. A PBN site with zero inbound links but dozens of outbound links to unrelated commercial sites screams manipulation. High IFR doesn't make a PBN safe, but low IFR makes it transparently disposable. Practical benchmarks matter here. Aim for at least 1:1 if you're building something that needs to survive beyond six months. Better operators target 3:1 or higher by publishing genuinely useful content that earns links, even if those links come from other properties in the network. The inbound links should come from diverse sources, aged domains, different IP ranges, and varied anchor text, not just reciprocal schemes within the same network. At Ottawa SEO, we stopped recommending PBNs around 2017 because the effort required to maintain defensible IFR ratios, unique content, and proper operational security costs more than building legitimate editorial relationships. A single well-placed guest post on a real publication with natural inbound links outperforms five PBN links with poor IFR. When clients ask about reviving old PBN infrastructure, we calculate the cost of bringing IFR above 2:1 versus allocating that budget to content partnerships. The math favours legitimate link building every time unless you're operating in a genuinely gray niche where editorial doors stay closed. Even then, one manual action wipes out years of PBN investment, while earned links persist.