Attach Rate
Attach rate is the percentage of customers buying a primary product who also purchase a complementary add-on — an extra module, a service tier, a seat upgrade, or an integration. It measures how effectively you expand the value of a customer beyond the initial sale, and because that expansion happens to people who have already bought, it's among the cheapest revenue you can generate.
Attach Rate = (Add-on Units Sold ÷ Primary Product Units Sold) × 100
If 200 customers buy your core product and 60 of them also take the premium analytics module, the module's attach rate is 30%. You track it per add-on, because each one tells you a different story about what your customers actually value once they're inside.
Why Attach Rate Matters
The economics are favourable for one reason: there's no new acquisition cost. You already paid to win the customer, so every add-on sale lands at a far higher margin than a net-new deal. That makes attach rate a direct lever on two metrics founders watch closely — it lifts average contract value (ACV) without a single extra lead, and the recurring expansion it drives is what pushes net revenue retention (NRR) above 100%, the point where your existing base grows faster than it churns.
A low attach rate usually signals one of two things: the add-on isn't packaged or surfaced at the right moment (a positioning problem), or it doesn't solve a real adjacent need (a product problem). The first is fixable with sales motion; the second isn't worth forcing.
How to Improve Attach Rate
The highest-leverage moment to sell an add-on is when the customer is already experiencing the problem it solves — at onboarding, at a usage milestone, or when they hit a limit on the core product. Bundling at the point of sale lifts attach rate but can mask which add-ons customers actually want; selling them separately, triggered by usage, produces a cleaner signal and often higher long-term retention. The reliable pattern is to tie the add-on offer to a moment of demonstrated need rather than a calendar date.
Because attach revenue expands existing accounts, it compounds: a higher attach rate raises ACV, which raises lifetime value and the LTV:CAC ratio, which in turn justifies spending more to acquire the next customer.
Related terms
Attach rate is part of the expansion-revenue picture alongside ACV (which it directly increases), net revenue retention (which it drives above 100%), MRR and ARR (where the recurring expansion shows up), and the LTV:CAC ratio (which improves as expansion lifts lifetime value).
Related Calculators
- MRR Growth Tracker — Expansion revenue from a higher attach rate compounds into MRR. Model how it changes your six-month trajectory.
- LTV & Churn Impact Calculator — Higher attach rate raises ACV and lifetime value. See the effect on your LTV:CAC ratio.