When it comes to your SMS program, we know list growth is one of the biggest priorities for a healthy and growing channel.
But not all opt-in rates are created equal. And depending on how you’re collecting numbers and what platforms you use, growth rates could be skewed or—even worse—inaccurately measuring your acquisition performance.
But listen. You can handle the truth.
So here’s what to pay attention to, along with questions to ask your provider, to accurately measure your list growth metrics.
True Definitions of Opt-in Rates
Opt-in rate is the percentage of website visitors who actively choose to subscribe to your SMS list. It's tempting to focus on a high opt-in rate, but there’s a few reasons why you can’t take this at face value.
For one, different popup vendors calculate opt-in rates differently, and this can significantly impact how you view your SMS growth. For example, your opt-in rates might be based on metrics that focus on submitted phone numbers rather than verified, fully completed opt-ins (subscribers). A verified opt-in is someone who submits their phone number and confirms their identity via a verification process like Onsite Opt-in, double opt-in, or two touch, for example.
Only SMS platforms can see which of these submissions actually follow through with opting-in after the initial step of entering their phone number. Otherwise, your rate might be looking at skewed rates that might include:
Failed Opt-ins: Submitted numbers that might never complete verification (e.g., replying Y or moving through the entire Onsite Opt-in OTP flow).
Duplicates: Counting users who are already subscribed, artificially inflating your reported opt-in rate.
Invalid Numbers: Numbers that are tied to a landline, or a false number such as “123-456-7890”
How Postscript Calculates Opt-in Rate
We use a simple, clear formula:
Subscriber Opt-ins / Total Popup Impressions
We don’t count all submissions, but instead focus on fully verified opt-ins, giving you the most accurate picture of your growth.
Opt-in Rate Alone Isn’t Enough
Subscriber count matters more than opt-in rate because it’s the outcome you’re aiming for that impacts key downstream metrics like clicks, conversions, orders, revenue, and unsubscribes.
Consider this scenario: You want to reach more visitors so you set your popup to target multiple pages of your site. This could lower your opt-in rate percentage (due to increased impressions), but your actual subscriber count might still rise significantly.
If you're only monitoring your opt-in rate, you might think performance dropped, when you've actually grown your subscriber base. This is so important to getting an accurate head count!
Let’s walk through it with some real numbers:
Platform A is showing that their popup has seen 10,000 impressions and 1,200 phone number submissions, which by their calculation would provide a 12% opt-in rate. However, in your Postscript dashboard, you only see 650 new SMS subscribers. Effectively, this would mean your opt-in rate is actually 6.5% because of things like failed opt-ins, invalid numbers, duplicates, etc. In this example, your conversion rate appears to be lower, but the number of overall opt-ins is the source of truth.
At Postscript, your popup sees 10,000 impressions as well, and drives 800 opt-ins. With this information, we can confidently say that your opt-in rate is 8%. While this rate does appear to be lower than the opt-in rate Platform A is providing, the number of successful SMS opt-ins is higher.
Questions to Ask Your Popup Provider
Here are a few questions to ask your current popup vendor to make sure your list growth is being measured correctly.
How do you calculate opt-in rate?
Understanding the specific formula will help you evaluate the validity of the reported rate.
Are you measuring submissions or actual completed opt-ins?
It's important to clarify whether the vendor tracks only initial submissions or verified subscriptions.
Remember, only verified subscriptions can be compliantly texted!
Does this measurement truly reflect subscriber growth?
Challenge the vendor to demonstrate the correlation between the reported opt-in rate and actual list growth.
What steps do you take to prevent skewed data around failed opt-ins and duplicates?
Inquire about the measures in place to ensure the accuracy of subscriber data.
We’re The List Growth Experts for a Reason
With Postscript, you get transparent metrics and powerful growth tools designed specifically for SMS, a combination you won’t find anywhere else.
Onsite Opt-in: Postscript patented technology proven to grow your list up to 3x faster.
Onsite Opt-in Reminder: An exclusive-to-Postscript feature ensuring visitors complete their subscription by sending them a follow up “Reply Y” text.
Fondue Integration: Provide compelling CashBack incentives that turn browsers into subscribers.
New Popup Editor: Intuitive, customizable, and built for conversion.
Within our Popup Analytics dashboard, you can easily see your engagement, impressions, and conversions so you can understand the effectiveness of your popup strategy at any given time. We also offer Enhanced Analytics via the Trends tab for customers on our Professional and Enterprise plans.
Best of luck on your list growth journey. May the best opt-in metrics be with you. And if they’re not—book a call with us.
