You finally added that "Text us JOIN to 55555" popup to your site. You got 2,000 subscribers in a week. You sent your first promo blast, and 400 of them immediately replied STOP. (For the full playbook, see our SMS marketing best practices and 10 text message examples that actually drive sales.) Pair SMS with email automation for maximum impact.
Congrats. You just burned through 20% of your list in one message.
SMS opt-in best practices aren't just about following the rules (though you should do that too, unless you enjoy $500 fines per text). They're about collecting subscribers who actually want to hear from you. Wild concept, I know.
Single Opt-In vs. Double Opt-In: Pick Your Poison
Here's the question nobody wants to answer honestly: should you use single or double opt-in for SMS?
Single opt-in means someone enters their number, and they're on your list. Done. Fast. Easy. Also how you end up with a list full of typos, fake numbers, and people who forgot they signed up three weeks later.
Double opt-in means they enter their number, get a confirmation text, and have to reply YES. More friction. Fewer subscribers. But every single person on that list chose to be there twice.
| Method | Conversion Rate | List Quality | Compliance Risk |
|---|---|---|---|
| Single Opt-In | Higher (15-25%) | Lower, more unsubscribes | Moderate |
| Double Opt-In | Lower (8-15%) | Much higher, fewer complaints | Low |
The TCPA (Telephone Consumer Protection Act) technically requires "express written consent" for marketing texts. A double opt-in gives you a paper trail. A single opt-in gives you a headache and potentially a class action lawsuit.
My recommendation? Double opt-in. Always.
Losing 10% of signups upfront beats losing your entire SMS program to a compliance violation.
What Your Opt-In Message Actually Needs to Say
Most brands treat the opt-in confirmation like an afterthought. "Reply YES to subscribe." That's it. No context, no expectations, no personality.
Here's what the TCPA and CTIA guidelines actually require in your opt-in disclosure:
- Your brand name. People need to know who's texting them.
- Message frequency. "Up to 4 msgs/month" not "we'll text you sometimes."
- Message and data rates disclaimer. Yes, it's obvious. Include it anyway.
- How to opt out. "Reply STOP to unsubscribe" in every single message.
- Link to your privacy policy. Non-negotiable.
Skip any of these and you're playing compliance roulette. The fines range from $500 to $1,500 per unsolicited message under TCPA. Send 10,000 texts without proper consent? Do the math. Then cry.
A good confirmation message looks like this:
"Acme Co: You're in! Expect 2-4 texts/month with deals and drops. Msg & data rates apply. Reply STOP to opt out. Privacy: acme.co/privacy"
Not sexy. But compliant. And compliant is the new sexy when your competitor just got hit with a $2.1 million TCPA settlement.
5 Opt-In Methods That Actually Work
Throwing a generic popup on your homepage and hoping for the best is not a strategy. Here are five methods that real brands use to build SMS lists without annoying everyone.
1. Checkout Opt-In Checkbox
Add a checkbox during checkout: "Text me shipping updates and exclusive offers." This works because the person is already giving you their phone number. You're just asking permission to use it.
Conversion rate: 25-35% when pre-unchecked (opt-in, not opt-out). Pre-checking the box is a dark pattern and potentially illegal depending on your jurisdiction. Don't.
2. Keyword Campaigns
"Text DEALS to 55555" on your packaging, receipts, or in-store signage. This is the OG method and it still works because it requires zero web interaction.
Conversion rate varies wildly, but retail brands report 5-15% of in-store customers opting in when signage is visible at checkout.
3. Pop-Up With an Incentive
"Get 15% off your first order. Enter your phone number." Everyone does this because it works. The trick is making the incentive specific enough to be compelling but not so generous that you attract deal-hunters who'll STOP after the discount.
A 10-15% discount or free shipping converts 2-3x better than "be the first to know about sales." People want tangible value, not vague promises.
4. Email-to-SMS Cross Promotion
Already have an email list? Send a campaign specifically asking subscribers to join your SMS list. These people already trust you, so conversion rates are significantly higher, often 8-12% of your email list.
The key: explain what they'll get via text that they won't get via email. Early access, flash sales, back-in-stock alerts. Give them a reason to hand over their phone number.
5. QR Codes in Physical Locations
QR codes made a comeback and they're perfect for SMS opt-in. Scan the code, pre-populated text message opens, hit send. Frictionless.
Restaurants, retail stores, and event venues see 10-20% scan-to-opt-in rates when the QR code is paired with a clear value proposition. "Scan for 20% off" beats "Scan to join our list" every time.
The Timing Trap: When to Send After Opt-In
Someone just gave you their phone number. You're excited. So you immediately blast them with three messages in two hours.
Stop.
The first 48 hours after opt-in determine whether someone stays on your list or hits STOP. Here's the sequence that works:
Immediately: Send the confirmation/welcome text with their discount code or promised value. This is expected. Deliver it instantly.
24 hours later: One follow-up. "Your 15% off expires in 48 hours" or a product recommendation. Something useful, not just noise.
Then wait. Your next message should be part of your regular cadence (2-4x per month for most brands). Resist the urge to send daily.
According to Attentive's benchmark data, brands that send more than 6 messages per month see opt-out rates jump by 28%. The sweet spot for most ecommerce brands is 4-6 messages per month. For non-ecommerce, 2-4.
Compliance Isn't Optional (But Most Brands Treat It That Way)
Let me be blunt: SMS compliance is not a suggestion. It's federal law.
The TCPA has been around since 1991 and it has teeth. Recent enforcement actions have produced settlements north of $100 million. This isn't the CAN-SPAM Act where the worst case is a sternly worded email from the FTC.
Here's your compliance checklist:
- Get explicit consent before sending. Not implied. Not "they gave us their number for shipping." Explicit, documented, marketing-specific consent.
- Honor STOP requests immediately. Not "within 24 hours." Immediately. Your platform should handle this automatically, but verify it actually works.
- Include opt-out instructions in every message. Every. Single. One.
- Keep records of consent. Timestamp, method, IP address, exact language they agreed to. Keep these for at least 5 years.
- Don't buy SMS lists. I cannot stress this enough. Purchased phone numbers come with zero consent. Texting them is literally illegal.
If you're using Klaviyo, Attentive, Postscript, or any major SMS platform, most of this is built in. But "the platform handles it" is not a defense if your implementation is wrong.
Measuring What Actually Matters
Subscriber count is a vanity metric. Here's what to actually track:
| Metric | Good | Bad | Why It Matters |
|---|---|---|---|
| Opt-out rate per campaign | Under 2% | Over 5% | Tells you if content is relevant |
| Click-through rate | 15-25% | Under 10% | SMS should outperform email by 3-5x |
| Revenue per message | $0.10+ | Under $0.03 | The only metric your CFO cares about |
| List growth rate | 5-10%/month | Flat or negative | Healthy lists grow consistently |
| Time to first purchase | Under 7 days | Over 30 days | Measures opt-in quality |
If your opt-out rate spikes after a specific campaign, that campaign was the problem. If it's consistently high, your entire SMS strategy needs a rethink.
The brands crushing SMS marketing aren't the ones with the biggest lists. They're the ones with the most engaged lists. A 5,000-person list where 80% open and 20% click will outperform a 50,000-person list where 30% open and 3% click.
Every time.
FAQ
What is SMS opt-in and why does it matter?
SMS opt-in is the process of getting explicit permission from someone before sending them marketing text messages. It matters because it's legally required under the TCPA, and because texting people who didn't ask to hear from you is the fastest way to destroy your brand reputation and get fined.
What's the difference between express and implied consent for SMS?
Express consent means someone specifically agreed to receive your marketing texts, usually by entering their number and checking a box or replying to a keyword. Implied consent (like having someone's number from a purchase) is not enough for marketing messages under TCPA. You need express written consent. Period.
How many texts per month should I send subscribers?
Most brands find the sweet spot at 4-6 messages per month for ecommerce and 2-4 for other industries. Going above 6 per month typically increases opt-out rates by 25-30%. Start conservative and increase based on engagement data, not gut feeling.
Can I add existing customers to my SMS list?
Not without their explicit consent for marketing messages. Having someone's phone number from an order doesn't give you permission to text them promotions. You need to re-engage them through email or other channels and get proper SMS opt-in first.
What happens if I send texts without proper opt-in?
TCPA violations carry fines of $500-$1,500 per message. Class action lawsuits are common and settlements regularly reach millions. Beyond legal risk, carriers can block your number entirely, killing your SMS program overnight.