If you're offering insurance to your customers, attach rate is the single number that tells you how well it's working. It's also the number most partners measure loosely or not at all. This guide covers what attach rate really is, how to calculate it without fooling yourself, and the concrete levers that move it.
What is insurance attach rate?
Attach rate is the percentage of eligible customers who actually buy insurance through your offer. It answers a simple question: of the people who could have taken coverage at the relevant moment, how many did?
The basic formula is:
Attach rate = bound policies ÷ eligible customers
The word that does the heavy lifting is eligible. Attach rate isn't measured against your entire customer base — it's measured against the people who actually hit the insurable moment. Get the denominator wrong and the number becomes meaningless.
How do you calculate it correctly?
Most attach-rate mistakes come from a sloppy denominator. Be deliberate about who counts as eligible.
- Define the insurable moment. Decide exactly which event makes a customer eligible — a vehicle purchase, a lease signing, a completed checkout.
- Count eligible customers in a period. How many people hit that moment in the month or quarter?