The headline finding
Across 4,000+ campaigns, we ranked subject lines into quintiles within each brand (top 20% = winners, bottom 20% = losers) for three different metrics: open rate, click rate, and revenue per recipient. We then aggregated which patterns showed up more often in winners vs. losers, portfolio-wide.
The result is the most useful insight in the dataset, and it's not a single “winning formula” — it's that the patterns that drive opens are the OPPOSITE of the patterns that drive clicks and revenue.
| Pattern | Opens | Clicks | Revenue |
|---|---|---|---|
| ALL-CAPS words | −9.6pp lose | +10.6pp win | neutral |
| Numbers in subject | −20.0pp lose | +6.2pp win | neutral |
| % / discount mention | −19.0pp lose | +5.3pp win | +5.3pp win |
| Urgency language | −7.7pp lose | +5.5pp win | +6.7pp win |
| Exclamation points | −5.0pp lose | +7.5pp win | +5.8pp win |
| Questions | +5.5pp win | neutral | −5.8pp lose |
Reading the table: “+10.6pp” means the pattern shows up 10.6 percentage points more often in top-quintile campaigns than bottom-quintile campaigns for that metric, within each brand.
There is no universal “good subject line.” It depends on what you're trying to do.
The clean rule
- Promo / sale emails → urgent + numbers + caps + exclamation. Yes, even the “spammy” subject lines. They convert.
- Content / nurture / brand emails → soft + curious + question-driven. Skip discount language entirely.
- Length doesn't matter. Median is 34-35 characters across every quintile of every metric. Stop A/B testing length. Start A/B testing tone.
Why this matters: brands that optimize subject lines for opens (the most-tracked metric) end up with engaged audiences who don't buy. Brands that A/B test for revenue learn that ugly, urgent subject lines convert. The dashboard your team stares at every morning is probably misaligned with the metric that pays the bills.
Subject lines that win opens
Top-quintile open rate: 66.0% median. Bottom quintile: 48.5% median. The gap is large, and the patterns that drive it are softer than instinct suggests.
- Question marks win (+5.5pp), question words at the start win (+3.8pp), questions at the end win (+4.3pp).
- Numbers, percent signs, and discounts lose — discount mentions show up almost 3x more often in losers than winners. Anything overtly transactional in the subject line drags opens down.
- ALL-CAPS, urgency language, exclamation points all lose. They read as promo and your audience filters them.
Subject lines optimized for opens look like a friend asking a question. They don't look like a Black Friday email.
Subject lines that win clicks
Top-quintile click rate: 0.72% median. Bottom quintile: 0.20% median. Almost everything that lost on opens wins on clicks.
- ALL-CAPS words show up +10.6pp more often in click winners — the single largest pattern delta in this analysis.
- Exclamation at the end (+8.7pp), exclamation anywhere (+7.5pp), urgency language (+5.5pp), and curiosity hooks (+6.3pp) all push clicks up.
- Numbers and percentage signs bring clicks too (+6.2pp / +5.3pp). The reader who clicks already knows it's a promo — being explicit pre-qualifies them.
- “You / your” loses on clicks (-4.3pp). Counterintuitive, but the data is consistent: vague second-person framing reads as bulk and gets ignored.
Subject lines that win revenue
Top-quintile revenue per recipient: $0.150 median. Bottom quintile: $0.013 median. The top quintile earns over 11x what the bottom does, per recipient.
- Urgency language is the biggest revenue lever — +6.7pp delta, the largest in the revenue analysis.
- Exclamation at the end (+7.5pp), discounts mentioned (+5.3pp), 30%+ discount specifically (+4.3pp) — explicit, urgent, transactional language wins on revenue.
- Questions actively lose on revenue (-5.8pp). The same patterns that win opens hurt the bottom line.
- Period at the end loses (-5.0pp) — declarative, soft endings underperform explicit calls to action.
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Methodology
Sample: 4,000+ DTC & subscription brand email campaigns.
Quintile method: For each metric (open rate, click rate, revenue per recipient), each brand's campaigns are sorted into quintiles. Top 20% = “winners,” bottom 20% = “losers.” Pattern prevalence is then aggregated portfolio-wide. This controls for brand-specific baselines so a high-performing brand doesn't skew the comparison.
Reading deltas: “+5.5pp” means a pattern shows up 5.5 percentage points more often in top-quintile campaigns than in bottom-quintile, within each brand. Not 5.5%. Percentage points.
Caveats: Apple Mail Privacy Protection inflates open rates and makes them noisier than they used to be. Click rate and revenue per recipient are the more reliable winner-vs-loser signals. The patterns above replicate within and across brands, but individual brand audiences may have idiosyncrasies — A/B testing your own list against these rules will tell you which apply most strongly to your subscribers.
About the author
Devyn Pukteris leads lifecycle at Sweat Pants Agency, where she builds Klaviyo-led email and SMS programs for DTC and subscription brands.
See more on email marketing, Klaviyo, and case studies from our portfolio.