Click to Open Rate: The Formula and How to Read It After Apple Privacy

Click to open rate (CTOR) is the share of people who opened an email and then clicked a link in it: unique clicks divided by unique opens. Apple Mail Privacy Protection can trigger opens nobody made, which inflates that denominator and pulls CTOR down. Hayes Media, an email and SMS retention agency for eCommerce brands, reads CTOR next to click rate and placed orders per recipient, never alone.

What's click to open rate?

Click to open rate tells you how many of the people who opened an email went on to click something in it. Open rate asks whether people opened. Click rate asks whether recipients clicked. CTOR asks a narrower question: once someone opened this email, did the content give them a reason to click?

Klaviyo's benchmarks guide lists the same ratio under a different name. It defines click-through rate as the "Percentage of people who click a link in your email out of the people who open your email." Other tools call it click to open rate or CTOR. Whatever the label, check the denominator. If it's opens, you're looking at CTOR. If it's recipients, you're looking at click rate.

What's the click to open rate formula?

Click to open rate = unique clicks divided by unique opens, times 100.

Use unique counts, meaning people rather than events. One subscriber who clicks five links counts once, and one subscriber who opens an email three times counts once. Klaviyo's definitions count people too.

Click rate keeps the same top line and swaps the bottom: click rate = unique clicks divided by emails delivered, times 100. Open rate puts opens on top and also divides by delivered: open rate = unique opens divided by emails delivered, times 100. Klaviyo describes open rate as the "Percentage of people who open your email out of those who receive it." What's happened to open rate itself is covered in our guide to email open rate benchmarks, so this page sticks to CTOR.

Pull all three numbers from the same report and the same date range, so the counts match.

A worked example (made-up numbers)

These numbers are made up to show the mechanism. They aren't from a client or a benchmark.

Say a campaign is delivered to 10,000 subscribers. Of those, 2,000 people really open it. Apple's privacy feature logs another 2,000 opens from inboxes where nobody read it, so the report shows 4,000 unique opens. Then 300 people click, and 40 place an order.

Reported CTOR. 300 clicks divided by 4,000 opens is 7.5%.

CTOR on real opens. 300 divided by 2,000 is 15%. You can't read this number off a report, because the report can't separate the two kinds of open.

Click rate. 300 clicks divided by 10,000 delivered is 3%.

Placed orders per recipient. 40 orders divided by 10,000 delivered is 0.4%.

Now say you send a similar email to the same list months later, and more of your subscribers have the privacy feature switched on. Reported opens rise to 5,000. Clicks stay at 300 and orders stay at 40. CTOR falls to 6%, while click rate holds at 3% and orders per recipient hold at 0.4%. The email didn't get worse. The denominator grew.

Why does Apple Mail Privacy Protection drag click to open rate down?

Apple's iPhone guide says Mail Privacy Protection "prevents senders from seeing if you've opened the email message they sent you." On a Mac, Apple says the Protect Mail Activity setting will "privately download remote content in the background when a message is received (instead of when you view it)."

Opens are tracked with an image. Klaviyo's conversion tracking guide says it tracks opens by "placing a tiny, invisible pixel image at the bottom of every email." Its guide to privacy opens says that when a recipient has the feature on, "all images in the messages they receive will be preemptively loaded," which "artificially inflates your open rates."

Clicks are tracked another way. Klaviyo says it "tracks click activity by adding unique tracking information to each URL," and Apple's guide notes that Mail Privacy Protection "does not extend to links." So the top of the CTOR fraction stays tied to people who clicked, while the bottom picks up automatic opens. More opens over the same clicks gives you a lower CTOR.

Can you strip Apple opens out of CTOR?

Not from the standard report. Klaviyo tags every open event with a property called Apple Privacy Open, which is "either True or False for all open events," and its email metrics reference suggests a custom report with that property to see how your opens are affected. That sizes the problem. It doesn't hand you a clean CTOR, because Klaviyo says an open flagged True "could have been opened by the inbox or by a recipient, and there's no way to differentiate between the two."

The counts don't line up perfectly from the other side either. Klaviyo notes that "It is possible for a recipient to click an email without opening it," for example by clicking before the email has fully loaded.

How should an eCommerce brand read click to open rate now?

Read it as one of three numbers, side by side, for the same send.

Click rate. Unique clicks divided by delivered. Neither side of this fraction counts automatic opens, so it's the steadier read on whether the email earned a click.

Placed orders per recipient. Orders attributed to the email divided by delivered. It shows whether the email moved people to buy. Klaviyo's closest metric is placed order rate, and its benchmarks guide defines conversion rate as the "Percentage of people who place an order after interacting with your email out of the people who receive your email." Check one setting before you trust it: Klaviyo's conversion tracking guide says conversions are tracked "if Apple Mail Privacy Protection (MPP) automatically opens the email," unless you adjust a setting to exclude those opens.

CTOR. Use it to judge the content once the email was opened, and compare it only against sends to a similar audience over a similar period.

Then read them together. If click rate and orders per recipient hold while CTOR falls, the change is in the denominator, as in the worked example. If click rate and CTOR fall together, the email is earning fewer clicks, and the content, the offer, or the audience needs work. If CTOR is healthy but orders per recipient is weak, people are clicking and not buying, so look past the email at the landing page, the price, or the stock.

When is click to open rate still useful?

Testing two versions of the content. When you split one audience at random and send both versions at the same time, both sides should carry a similar share of automatic opens, so a CTOR gap points at the content. Pick the winner on click rate or orders where your platform lets you, and use CTOR to explain why it won.

Checking the body of a flow email. A flow email that gets opened but rarely clicked has a content problem, and CTOR flags it. Our abandoned cart email examples show the plain version of a first reminder: the product photo, one line, and one button back to the cart.

Spotting one weak send. If CTOR drops on one campaign while your other sends that week hold steady, the cause sits in that email.

When does click to open rate mislead?

Subject line tests. A subject line changes who opens, and automatic opens land in the denominator whatever the subject says. Don't pick a subject line winner on CTOR. Pick it on click rate or orders where your platform lets you.

Month over month trends. As the share of your list with the privacy feature on changes, CTOR moves with no change in the email. Check click rate for the same period before you act on a CTOR trend.

Comparing segments. A segment with more privacy-protected inboxes carries more automatic opens, so its CTOR can look weaker even if its people click just as often.

Small sends. With a few hundred opens, a handful of clicks swings the percentage a long way. Compare sends of a similar size, or pool several sends before you read a change.

When doesn't CTOR matter?

If your email isn't reaching the inbox, CTOR is the wrong place to start. Deliverability is the first part of the email marketing audit we run before taking any client: authentication, spam complaint trends, and whether engagement has drifted down over months. Fix that before you tune content.

CTOR is an email metric, so it doesn't apply to SMS. Judge texts on clicks and orders.

For flows, CTOR helps you diagnose a weak email, but it isn't the scoreboard. Our guide to the Klaviyo flows every store needs judges the whole set on repeat purchase rate, time to second order, and the revenue the flows drive. Our welcome series guide lists judging that flow on open rate as a mistake, and CTOR shares the same inflated opens in its denominator.

How Hayes Media reads email performance for your store

Hayes Media builds and runs retention for eCommerce brands: email, SMS, loyalty programs, and subscribe-and-save. We work in Klaviyo for most accounts and have experience in most other email and SMS platforms. Email on its own is a full engagement with us, and you can see how our email and SMS service works.

Our retention site lists "$500M+ Client revenue driven" and says we're "Trusted by 50+ eCom brands". Those figures, like our case studies, are published by Hayes on its own sites. We don't have a third-party review profile or a Klaviyo partner listing.

Hayes Media works with brands doing at least $100K per month in revenue. It's a guideline, not a gate: a smaller brand with a clear budget set aside to scale and real order volume already qualifies.

One-time email projects start from $2,000 USD, and retainers for ongoing full management start from $4,000 USD per month, scoped on the discovery call.

If you want to know what your click numbers are really saying, we'll audit your account and lay out CTOR, click rate, and placed orders per recipient for your flows and campaigns side by side, plus what to fix first. Book a discovery call. No onboarding fees. No lock-in contracts. No junior marketers.

Sources

Apple Support: Use Mail Privacy Protection on iPhone. Source for Mail Privacy Protection hiding whether an email was opened, and for it not extending to links.

Apple Support: Change Privacy settings in Mail on Mac. Source for Protect Mail Activity downloading remote content in the background when a message arrives.

Klaviyo Help Center: How to identify iOS15 Mail Privacy Protection opens. Source for preloaded images, inflated open rates, and the Apple Privacy Open property.

Klaviyo Help Center: Email metrics reference. Source for the custom report suggestion for privacy opens.

Klaviyo Help Center: Getting started with benchmarks reports. Source for Klaviyo's definitions of open rate, click-through rate, and conversion rate.

Klaviyo Help Center: Understanding message conversion tracking. Source for pixel open tracking, link click tracking, clicks without opens, and conversions counting automatic Apple opens.

Hayes Email and Retention. Source for the Hayes retention figures quoted above, which Hayes publishes itself.