--- title: Click-to-Open Rate (CTOR) — definition | RGM® Glossary url: https://realgrowthmatters.com/glossary/click-to-open-rate/ updated: 2026-06-10 source_html: https://realgrowthmatters.com/glossary/click-to-open-rate/ --- # Click-to-Open Rate (CTOR) click-to-o·pen rate/klɪk tɪ ˈoʊpən ɹeɪt/noun Of the people who opened, how many cared? — the content-quality metric opens can't fake. Mostly. Term : Click-to-Open Rate Abbreviation : CTOR Formula : Unique clicks ÷ unique opens Post-2021 caveat : Denominator inflated by Apple MPP ## Forms & parts of speech CTOR · acronym Clicks over opens. "CTR is flat but **CTOR** fell by a third — the list still opens, the content stopped landing." ## Definition in plain terms Click-to-open rate divides unique clicks by unique opens: of the people who (apparently) saw the email, what share clicked? Where click-through rate (clicks ÷ delivered) blends list quality, subject line, and content into one number, CTOR isolates the content question — did the message earn action from its actual audience? An email delivered to 10,000, opened by 3,000, clicked by 450 has a 15% CTOR. ## The mechanics CTOR's diagnostic power is the separation: low open rate with high CTOR means a targeting/subject problem wrapped around good content; high opens with low CTOR means the envelope writes checks the letter can't cash. The 2021 caveat is structural — Apple's Mail Privacy Protection inflates the open denominator with machine opens, DEFLATING measured CTOR for Apple-heavy lists. It remains useful for trend comparison within a stable list and for relative judgments between sends; absolute cross-list benchmarks died with honest opens. ## When it matters CTOR matters as the email program's content-quality meter — the number that arbitrates between 'our newsletter is boring' and 'nobody sees it.' Segment-level CTOR finds where relevance decays (engaged-cohort CTOR triple the tail's = a list-hygiene mandate). Post-MPP, sophisticated teams either filter machine opens where their ESP supports it or quietly migrate CTOR's job to click-per-delivered trends — keeping the QUESTION while replacing the compromised denominator. **Worked example.** A media company's newsletter holds a steady 42% open rate while revenue per send sinks. The CTOR cut tells the story opens hid: 18% to 7% over two quarters — readers still open from habit, but the content stopped earning clicks. The rebuild runs on CTOR as judge: subject lines stop overpromising (closing the envelope-letter gap), the link hierarchy drops from fourteen to four, and each section gets a CTOR target. Two months later CTOR recovers to 14% and revenue follows — the audience was never lost, just bored. **Failure modes to watch.** Benchmarking absolute CTOR across lists post-MPP; reading low CTOR as a list problem when it's a content problem; stuffing more links in to chase clicks; and ignoring the machine-open denominator drift. ## Synonyms & antonyms ### Synonyms CTORclick-to-open rate ### Antonyms CTR (clicks per delivered)unclicked opens ## Origin & history \*No verifiable first use is documented; the account is built from how the field adopted the term. CTOR emerged from 2000s email-marketing analytics as ESPs sought a content metric independent of list size — the clicks-over-opens ratio became a standard dashboard line as the industry matured, and survives (with caveats) the 2021 machine-open era. Etymology: [source](https://en.wikipedia.org/wiki/Email_marketing). ## Usage trends Search interest for this term over the last five years: [View interest-over-time on Google Trends →](https://trends.google.com/trends/explore?q=click%20to%20open%20rate&date=today%205-y) ## Common questions What is click-to-open rate? : Unique clicks divided by unique opens — how well the content converted the audience that actually saw the email. How does CTOR differ from CTR? : CTR divides clicks by delivered (whole-funnel); CTOR divides by opens, isolating content effectiveness. How did Apple MPP affect CTOR? : Machine-generated opens inflate the denominator, deflating measured CTOR — trend comparisons within a list survive; absolutes don't. ## Related tools & calculators - tool[Funnel drop-off analyzer](/tools/funnel-drop-off-analyzer/) ## Resources & people to follow - referenceLitmus — MPP-era email analytics guidance - referenceMailchimp/Campaign Monitor — CTOR benchmark methodology - referenceRGM analysis — migrate CTOR's job to click-per-delivered trends post-MPP Curated, non-competitor resources verified per term. ## Related training - module[Marketing analytics](/training/marketing-analytics/) ## Disciplines Areas of marketing where click-to-open rate (ctor) is a core concern: [Measurement](/training/marketing-analytics/)[Growth strategy](/training/growth-marketing-foundations/) ## Read next ## Related terms [Open rate](/glossary/open-rate/)[Email marketing](/glossary/email-marketing/)[Unsubscribe rate](/glossary/unsubscribe-rate/)[Conversion rate](/glossary/conversion-rate/)[Ann Handley](/glossary/ann-handley/) ## Sources 1. trends[Google Trends — "click to open rate"](https://trends.google.com/trends/explore?q=click%20to%20open%20rate&date=today%205-y)