B
Evidence Grade B
Graded
under review
Safe to Cite
Current
17%
17% -- email click through rate lift for Email campaigns using 'free' in the subject line (HubSpot A/B test) (2026)
Attribution:
View source
Lighthouse Research Team
Last verified:
·
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Source verified
Evidence graded
Value
17%
Unit
Percentage
Data Vintage
2026
Entity
Evidence Quality
B
Strong, reliable evidence
Sourced from a well-regarded research firm or industry leader with transparent methodology and a reasonably large sample.
Single source - not yet corroborated
Score breakdown
Extraction
50
Source Trust
60
Citation Chain
20
Independence
30
Methodology
45
Freshness
95
Source
HubSpot
Primary
Tier C
https://www.3d2b.com/blog/marketing-services-systems/email-marketing/5-ways-to-supercharge-your-resu… ↗
Source Article
3D2B - 5 Ways to Supercharge Your Results from B2B Email Marketing
Original Research
HubSpot
· Original study ↗
Methodology
HubSpot A/B test found that using the word 'free' in the subject line had only a minor negative effect on deliverability, which was outweighed by a 17% increase in click-through rates. Cited secondhand by 3D2B.
Methodology documented
Segmentation
IndustryB2B
RoleAll marketers
Channelemail
Cite this stat
Plain Text
Email campaigns using 'free' in the subject line (HubSpot A/B test): 17% email click through rate lift. Source: HubSpot (2026). Via Lighthouse Intelligence -- https://lighthousedata.io/data/free-subject-line-ctr-lift
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<blockquote cite="https://lighthousedata.io/data/free-subject-line-ctr-lift" style="border-left:3px solid #2563eb;padding:12px 16px;margin:16px 0;font-family:system-ui,sans-serif;background:#f0f4ff;"><strong>17%</strong> -- email click through rate lift for Email campaigns using 'free' in the subject line (HubSpot A/B test)<br><small>Source: HubSpot (2026) · <a href="https://lighthousedata.io/data/free-subject-line-ctr-lift" target="_blank" rel="noopener">Lighthouse Intelligence</a></small></blockquote>
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