Cart Abandonment Email Subject Lines: How to Write and Test Them

The best cart abandonment email subject lines change with each send. The first reminder names the item that was left behind. Later sends add proof, answer the doubt that stopped the order, or give one honest reason to come back. Hayes Media, an email and SMS retention agency for DTC and Shopify brands, picks subject line winners on placed orders per recipient, never on opens. This guide covers the subject line and preview text for each send, then how to test them. For the full emails behind each send, see our abandoned cart email examples.

What makes a cart abandonment subject line work?

A good cart subject line tells the shopper which cart this is and what's in it, in words they'd use. It doesn't need to be clever. They added something to the cart, so the item is the most relevant thing you can show them in the inbox.

Klaviyo's own guide to abandoned cart flows makes the same point about the email itself: "Notice that the primary focus of the message is the item that the recipient left in their cart." The subject line should promise exactly what the email delivers. If the subject says "Your linen duvet cover" and the email opens on a sale banner, you've broken that promise in the first second.

Cart and checkout abandoners also need different lines. Klaviyo recommends running a flow triggered by Added to Cart and a separate one triggered by Started Checkout, because "Someone who starts checkout has shown stronger purchase intent than someone who only added an item to their cart, so you may want different timing or messaging for each." A checkout abandoner has already typed their details in, so their subject line can be more direct about finishing the order.

What should the first reminder's subject line say?

Name the item and say the cart is still there. That's the whole job. No countdown and no discount. The first send works when it makes the way back easy, and the subject line's part in that is being recognizable at a glance.

If your email platform can pull the product name from the cart event into the subject line, use it. If it can't, name the product category or your brand plus "your cart". Here are made-up examples for a store selling bedding:

Names the item. "Your linen duvet cover is still in your cart"

Asks plainly. "Still thinking about the linen duvet cover?"

For a checkout abandoner. "You're one step from your linen duvet cover"

Klaviyo's guide suggests urgency, giving "Hurry, before it sells out!" as an example. We'd only use a line like that when it's true, such as stock that's genuinely low. A shopper who sees "selling out" on every cart email learns to ignore it.

What should the second and third subject lines say?

The second send answers the question that actually stops orders in your category. That might be shipping cost, delivery speed, the returns window, sizing, or how you compare with a cheaper option. Pick one. The subject line names the answer, so a shopper who had that doubt sees it solved before they open. Your support inbox and product reviews show you which objection comes up the most.

Returns objection (made-up example). "Free returns on your duvet cover, no questions"

Proof objection (made-up example). "What 2,000 customers say about our linen"

Only use a number like that second example if it's real and you can show it in the email.

The third send is the honest last call. It says this is the last reminder and, only if your margins allow it, carries the one offer you're willing to make. Klaviyo's guide says "we don't encourage you to include a coupon in the first email" because it "can train customers to abandon carts in order to get the discount." Its suggestion is to "hold off until the final email, or only offer it to people who have never purchased before." Keep the offer out of the subject line on sends one and two, so shoppers don't learn that waiting gets them a code.

Last call, no offer (made-up example). "Last reminder about your cart"

Last call, with an offer (made-up example). "10% off your cart, in this email only"

How should preview text work with the subject line?

Preview text is the second line a shopper reads. Klaviyo describes it as text "displayed in the inbox after the subject line of an email" and warns that if you don't set it, "inboxes will automatically pull it from the first line of text within an email." That's how a cart email ends up previewing "View in browser" or your navigation menu.

Treat the subject line and preview text as one sentence split in two. The subject carries the main point. The preview adds a second fact the subject didn't have room for. It should never repeat the subject.

Send one (made-up example). Subject: "Your linen duvet cover is still in your cart". Preview: "We've saved it. One tap takes you back to checkout."

Send two (made-up example). Subject: "Free returns on your duvet cover, no questions". Preview: "Try it on your bed for a month. Send it back if it's not right."

Send three (made-up example). Subject: "Last reminder about your cart". Preview: "After this, we'll leave you to it."

Klaviyo also notes that "Different devices and email clients have different limits on the amount of preview text characters displayed, with smaller screens displaying fewer preview characters." Put the useful words first, so the line still makes sense when it's cut short on a phone.

How do you test cart subject lines without fooling yourself?

Judge a subject line test on placed orders per recipient or revenue per recipient. Don't judge it on open rate. Apple's iPhone guide says Mail Privacy Protection "prevents senders from seeing if you've opened the email message they sent you." Klaviyo explains what that does to your numbers: for recipients with the feature on, "all images in the messages they receive will be preemptively loaded, whether the recipient opens the email or not," which "artificially inflates your open rates."

So when one subject line shows a higher open rate, part of that gap can be automatic loads, not people. Our guide to email open rate benchmarks covers what to read instead, and the click to open rate guide explains why you shouldn't pick a subject line winner on CTOR either.

Here's how to set a fair test in a Klaviyo flow:

Change one thing. Test two subject lines with the same preview text and the same email, or two preview texts with the same subject. If you change both, you won't know which one did the work.

Split the audience at random. Klaviyo lets you set "the weight of each variation to establish the percentage of recipients that will receive each email." An even split keeps the comparison clean. Leave the option to automatically choose distribution off, because Klaviyo says it will "direct more recipients to the better performing variation while the test is still running."

Know what the tool picks on. Klaviyo's flow A/B guide says "For flow emails, only Open Rate and Click Rate are available as winning metrics," and tests default to click rate. Click rate beats open rate, but it still isn't an order.

Read the order column. Klaviyo's results page shows "the attributed order value and the number of recipients who placed an order, rather than the placed order rate." Divide placed orders by recipients for each variation yourself, then use Choose Winner to pick on that.

End the test yourself. The automatic end on statistical significance is on by default, and Klaviyo says you can clear it "if you'd rather end the test manually or use only a date limit." Clear it, and wait until each variation has enough placed orders that the gap isn't down to a handful of buyers.

Fix the conversion setting first. Klaviyo's conversion tracking guide says conversions are tracked "if Apple Mail Privacy Protection (MPP) automatically opens the email," and that you can adjust a setting to exclude those opens. Change it before you trust any order count.

A worked example with made-up numbers

Say send one goes to 4,000 people per variation. Subject A, "You left something behind", shows a 52% open rate and 120 recipients who placed an order, which is 3.0% placed orders per recipient. Subject B, "Your linen duvet cover is still in your cart", shows a 44% open rate and 180 recipients who placed an order, which is 4.5%.

On opens, A wins. On orders, B wins by 60 orders out of the same 4,000 sends, a gap big enough that it isn't down to a handful of buyers. B is the one we'd keep, and the next test would try a new challenger against it. When you test an offer line on send three, check the margin on those orders too, because a discount can win on orders and still leave you with less profit.

Where does SMS fit in an abandoned cart flow?

A text has no subject line, so its first few words do that job. Our SMS marketing guide sets out the split we run: SMS sends "One short nudge with the cart link while intent is warm," and email carries the persuasion sequence. The text and the email never say the same thing at the same time.

Made-up example. "Your linen duvet cover is still in your cart: [link]" plus your brand name and the opt-out wording your consent setup requires.

Get consent right before the first text. The SMS guide covers the US consent rules. Klaviyo's own advice is to set up an email only abandoned cart flow first "to make sure everything is set up properly," then add SMS.

When doesn't this apply?

The flow isn't firing properly. A better subject line can't fix a flow that sends to the wrong people. Klaviyo's guide says to add the filter "Placed Order zero times since starting this flow" so buyers stop getting reminders, and to "turn off any default platform abandoned cart messages to prevent duplicating messages to customers." Our Klaviyo flows walkthrough covers the full flow map.

The shopper never added to cart. Someone who only viewed a product belongs in a different flow with a softer message. Our guide to the browse abandonment email flow covers who gets it and what it says.

Your flow sends too few emails to test. A split test needs enough orders on each side to show a real gap. If a month of sends only produces a handful of orders, write the best line you can with the patterns above and judge the flow as a whole instead.

Who does Hayes Media write cart flows for?

Hayes Media builds and runs email, SMS, loyalty programs, and subscribe-and-save programs for eCommerce brands, and email on its own is a full engagement. We work with brands doing at least $100K per month in revenue. That'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. Our retention site says we're "Trusted by 50+ eCom brands" with "8 yrs Retention expertise." Hayes publishes those figures and its case studies itself, and it has no third-party review profile or Klaviyo partner listing. See what's included on our email and SMS service page.

Want your cart flow subject lines checked?

Book a discovery call and we'll audit your cart and checkout flows: the subject line and preview text on every send, how your tests pick their winners, and what to fix first. No onboarding fees. No lock-in contracts. No junior marketers.

Sources

Klaviyo Help Center: How to create an abandoned cart flow. Source for the cart and checkout flow split, the item focus, the urgency example, the coupon advice, the Placed Order filter, and setting up email before SMS.

Klaviyo Help Center: How to A/B test a flow email. Source for variation weights, winning metrics, and ending a test manually.

Klaviyo Help Center: How to review email A/B test results for flows. Source for the order value and placed order columns in test results.

Klaviyo Help Center: How to insert preview text into an email. Source for where preview text shows and how inboxes fill it when it's not set.

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

Klaviyo Help Center: Understanding message conversion tracking. Source for conversions tracked on automatic Apple opens.

Apple Support: Use Mail Privacy Protection on iPhone. Source for what Mail Privacy Protection hides from senders.

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