What is attachment rate?
Attachment rate is the share of customers who buy an additional service on top of their core agreement. In commercial services the core is often an inspection or maintenance agreement, and the attached services are things like monitoring, extended coverage, backflow testing, kitchen hood suppression or water treatment. The general business term is attach rate: secondary products or services sold per primary sale.
Why it matters to a revenue leader
Attached services raise revenue per site without a new customer, and each extra service makes the relationship harder to replace at renewal. The U.S. Department of Energy's O&M guide gives a services example: owners on a full-coverage contract can add repair and replacement coverage for an additional fee. For a revenue leader at a PE-backed platform, attachment rate is often where an add-on acquisition's service lines meet the existing customer base, and the cross-sell case in the deal model depends on it.
How to calculate it
Attachment rate = customers with at least one attached service ÷ customers with a core agreement. A unit version counts attached services per core agreement.
Common mistake: measuring it across all customers, including sites that could never use the service, such as buildings without the equipment.
Example
Fictitious numbersA fire and life safety company has 2,000 sprinkler inspection customers, and 600 also buy fire alarm monitoring, a 30% attachment rate. After an add-on acquisition brings in kitchen suppression services, 120 of the 800 customers with commercial kitchens add it in the first year, a 15% attachment rate for that service.
"Which of our services has the lowest attachment rate among the customers who could use it?"
Sources
- Attach rate (Wikipedia) checked 9 Oct 2026
- O&M Best Practices Guide, Release 3.0, Chapter 3: O&M Management (U.S. Department of Energy, FEMP) checked 9 Oct 2026