Open rate is calculated as (Unique Opens ÷ Delivered Emails) × 100. It is one of the primary engagement metrics for newsletter creators. Industry benchmarks for creator newsletters typically range from 35–55% for engaged lists, though rates vary significantly by niche, list age, and sending frequency. A finance or B2B SaaS newsletter with a tightly scoped audience often sustains 45–60% open rates; a general lifestyle newsletter with rapid but less filtered list growth may settle at 25–35%. Apple Mail Privacy Protection (MPP), introduced in 2021 and now active on roughly 40–50% of email opens globally, inflates open rates by pre-fetching emails on Apple devices regardless of whether the subscriber actually views them. This means a newsletter reporting 55% open rate may have a true engagement rate closer to 35–40% once MPP phantom opens are subtracted. Treat open rate as a directional signal and monitor click rate alongside it — clicks are unaffected by MPP and give a more accurate read on genuine reader engagement. Factors that move open rate: subject line (the largest lever), preheader text, sender name recognition, send time, list age, and content consistency. Subject lines with specificity, a clear benefit, or a named topic outperform vague or overly clever ones in most creator niches. Send time matters less than commonly assumed — for tight editorial voices, subscribers open eventually regardless of time; for broadcast lists with weaker habituation, Tuesday–Thursday at 9–11am local time consistently outperforms weekends and late evening. For sponsorship pricing, many advertisers use open rate as a proxy for engaged impressions. A 40% open rate on 10,000 subscribers = 4,000 expected opens, which is the impression count used to calculate the sponsorship rate (4,000 × CPM ÷ 1,000 = sponsor price). InfluencersKit tracks opens alongside click rate and revenue metrics for a fuller picture, and surfaces a benchmark comparison so you can see how your rates compare to peers in the same vertical. Open rate optimization that actually moves the needle: test subject lines against your own audience rather than chasing generic best-practice lists. What works for a daily fintech briefing is different from what works for a weekly personal essay. Run A/B tests on two subject line variants with 20% of your list each, then send the winner to the remaining 60% — this takes five minutes to set up in most ESPs and compounds across every future send. Improving open rate by 5 percentage points on a 10,000-subscriber list generates 500 additional opens per send.