Before customers read your email, they make a split-second decision based on one thing: the subject line.
No matter how strong your offer is, it can’t perform if it never gets opened. In just a few words, it has to grab attention, spark curiosity, and give readers a reason to open now instead of scrolling past.
That’s where proven subject line formulas come in. Rather than guessing what might work, these formulas tap into real human behaviour to consistently boost open rates and engagement.
Below are five high-performing subject line formulas and simple structures you can reuse across campaigns.
5 Subject Line Formulas for Higher Loyalty Email Open Rates
1. Encourage Curiosity
Humans are naturally curious beings. When we sense there’s something valuable we don’t fully know yet, our instinct is to find out more.
Curiosity-based subject lines tap into this psychological trigger by hinting at a reward, insight, or opportunity without giving everything away. Instead of spelling out the offer, they create just enough intrigue to make opening the email feel necessary.
Subject Line Formula: Number or Tease + Outcome or Benefit (without full details)
When to use curiosity-based subject lines (with examples):
- Educational content: Perfect to create curiosity on blogs, case studies or other content. “One small action that unlocks bonus points.”
- New product releases: Build excitement on new product teases: “Something new is coming soon…”
- Value reminders: Highlight potential reward opportunities: “You’re closer to a free reward than you think…”
- Loyalty program tips: Encourage members to learn more about the value of your loyalty program: “This perk is hiding in your account.”
2. Emphasize Urgency
Urgency is a great way to get people to act fast (or at least open a little faster).
Urgency-based subject lines give customers a clear reason to open now instead of thinking, “Eh, I’ll look at this tomorrow.” By calling out limited time, expiring points, or last-chance rewards, you create that gentle nudge that says, don’t wait on this one.
Subject Line Formula: Action Verb + Deadline or Timeframe + Consequence or Reward
When to use urgency-based subject lines (with examples):
- Time-based bonus points events: When customers have a limited window to earn extra value, urgency reinforces the need to act quickly: “Ends tonight: 500 bonus points on order $50+”
- Limited-time products or offers: Perfect for seasonal items or short-lived promotions: “Last day to try our Candy Cane Hot Chocolate!”
- Expiring points/ rewards: Nobody likes losing their hard-earned points: “Last chance to use your points before they expire”
Pro Tip: DataCandy makes it easy to send expiring points and reward reminders automatically. Add one of these subject line tricks, and you’ll start seeing more opens, redemptions, and action from your loyalty members.
3. Ask Questions
Question-based subject lines feel conversational and invite the reader into a moment of self-reflection. Instead of telling customers what’s inside, you prompt them to think about their own situation.
Subject Line Formula: Are you / Did you / Ready to + Action or Reward?
When to use question-based subject lines (with examples):
- Re-engagement emails: Question format subject lines are great for win-back campaigns because they gently re-capture attention: “Did you forget about your rewards?” or “Ready for your free treat?”
- Abandoned cart nudges: Sometimes customers get distracted and forget to complete their purchase. A gentle reminder can bring them back: “Oops. Did you leave something behind?”
- Points or reward reminders: Questions work as soft nudges, encouraging customers to revisit and use their rewards: “Forgot to redeem your reward?”
Questions naturally engage the brain and encourage customers to open the email to find the answer (especially when the question feels personally relevant).
4. Highlight Exclusivity
Everyone likes to feel special. Exclusivity-focused subject lines tap into that feeling by making customers feel recognized and rewarded for their loyalty. Instead of sounding like a message sent to everyone, these emails feel personal (like a perk reserved just for them).
Subject Line Formula: Only for Members / Just for You + The Benefit
When to use exclusivity-based subject lines (with examples):
- Rewards for VIP tiers: Highlight status-based perks and reinforce the value of the membership: “VIP access: Spring sale starts today”
- Early access campaigns: Perfect for new product launches offered to select members: “Early access: Be the first to try our new lip gloss.”
- Surprise-and-delight moments: Unexpected rewards feel even more exciting when framed as exclusive: “This reward is reserved just for you”
When customers feel like they’re part of an inner circle, they’re far more likely to open and engage. That sense of belonging is at the heart of loyalty programs, and exclusivity reinforces the emotional value of being a member.
Read our full blog for tips and tricks on how to transform it into your highest revenue-generating email.
5. Add a Number
Numbers signal bite-sized, scannable content. They make the email feel easy to read and consume, which is perfect for busy inboxes. Plus, lists trigger curiosity and make readers want to see what they might be missing.
Subject line formula: Number + ways to + action or reward
When to use numbers-based subject lines (with examples):
- Educational content: Perfect for tips, guides or explainers that break information into digestible pieces: “5 reasons your points are worth more than you think”
- Loyalty tips and engagement campaigns: Ideal for encouraging ongoing participation: “7 easy ways to earn bonus points this month.” or “3 rewards you could unlock right now”
- Product usage ideas: Showcase versatility and educate customers on the benefits of your products: “3 recipes you can make with your dutch oven”
Number-based subject lines work because they set clear expectations right away. Customers instantly know what they’re getting, how long it’ll take to read, and why it’s worth their time.
Loyalty Email Subject Line Best Practices
Even the strongest formulas perform better when paired with smart execution.
Personalize Whenever Possible
Customers want to feel like an email was sent just for them, not blasted to a massive list. Using details like their name, points balance, or reward status makes it instantly more personal and much more likely to get opened.
Examples:
- “Alex, your points are about to expire”
- “Sarah, you’re 100 points away from a reward”
A/B Test Different Formulas
A/B testing takes the guesswork out of what works. Trying small variations helps you learn what your audience responds to most, so your final send is set up for success.
You can test things like:
- When emails are sent
- Different CTA wording
- Subject line styles
- Who the email appears to be from
Segment Your Audience
Not all customers are motivated by the same things, and one-size-fits-all email blasts just don’t cut it anymore.
When you segment your audience based on behaviour, visit frequency, purchase patterns, or loyalty tier, you can send messages that feel actually relevant to each group, instead of generic noise. This approach helps ensure your offers reach the right people at the right time and drives stronger engagement, higher open rates, and meaningful loyalty growth.
Final Thoughts
A strong subject line sets expectations, sparks interest, and gives customers a reason to engage before they even open the message.
By using these five subject line formulas, and pairing them with personalization, testing, and smart segmentation, you can turn everyday loyalty emails into high-performing touchpoints that drive opens, clicks, and real action.
Start small. Test one new formula in your next send. Pay attention to what your customers respond to, and build from there. With the right subject line strategy, your loyalty emails won’t just get opened, they’ll get results.
Read our guide where we cover 7 things to QA before hitting send to catch to catch mistakes before they happen.
