Net-new subscribers: are your popups growing your list?
Your opt-in rate tells you how many people submitted. It does not tell you how many of those emails were new. Some captures are genuinely new subscribers. Some are people who were already on your list and just typed their email again. Some are existing customers taking the discount one more time. The Capture Quality section in Analytics separates them, so you can see whether your popups are growing your list or re-collecting people you already had.
The question opt-in rate cannot answer
Three different people click “get 10% off”:
- Someone genuinely new, who was not on your list and had never bought. The discount bought you a relationship you did not have.
- Someone already subscribed, who cleared their cookies or is on a new device. You re-collected a name you already had, and gave a discount for it.
- An existing customer, who has bought before and now learns to expect the popup discount on the next order too.
Opt-in rate counts all three the same. Capture Quality tells them apart.
How SupaPop decides
The moment someone submits, SupaPop checks (at that instant, before adding them anywhere) whether the email was already in your Klaviyo list and whether the person was already a customer in Shopify, then records the answer. Checking at the moment of capture is the whole trick: a second later they are a subscriber, because you just added them, so the only honest reading is the one taken before you added them.
Reading the section
Open Analytics and find the Net-new Subscribers card and the Capture Quality section. Both appear once you have captures SupaPop could classify. The section sorts your captures into:
- Net-new subscribers: not on your list and not a customer. The growth you wanted.
- Already on your list: already subscribed, or we already had their Klaviyo profile. You re-collected someone you already had.
- Known, not subscribed: an existing customer who was not on your email list.
- Unknown: we could not classify them (captured before this was switched on, or the lookup was not available yet). Unknown captures are left out of the Net-new Subscribers percentage so the number stays honest.
Each row shows the captures, their share of classified captures, the attributed revenue, and the discount given. The heading also calls out the discount recycled to people you already had: the discount dollars that went to already-subscribed or existing customers. That is the margin you spent re-collecting people instead of acquiring new ones.
What to do with it
- Compare popups (in single-popup view). A homepage spin-to-win might be mostly net-new and worth every point of margin; an exit popup on the account page might be mostly existing customers and quietly costing you.
- Watch the recycled-discount figure. If a large share of your discount is going to people you already had, that is a reason to rethink who sees the offer, or whether those segments need a discount at all.
- Read a high net-new rate as the popup doing acquisition, and a high already-had rate as the popup mostly re-engaging people. Re-engaging can be fine. The point is to know which one you are paying for.
One honest caveat
This measures list overlap, not cause. “Net-new” means the email was new to your list at the moment of capture. It does not prove the popup caused a sale that would not have happened anyway. Proving that needs a holdout test (showing the popup to some visitors and not others, then comparing the two groups). Read Capture Quality as a measure of capture quality and discount leakage, not as proof of incremental revenue.
Requirements and notes
- The “already on your list” reading comes from Klaviyo, so connect Klaviyo under Settings for the most accurate result.
- The existing-customer reading comes from Shopify. After this feature rolls out, your store approves a new permission the next time you open the SupaPop admin; until then the customer column reads “unknown” and everything else still works.
- Captures from before this was switched on show as “unknown” and are excluded from the rate, so early numbers reflect only recent captures.
For the full dashboard tour, see Understanding your analytics.