Added to Cart vs Checkout Started in Klaviyo

For ecommerce operators, the choice between Added to Cart and Checkout Started as flow triggers in Klaviyo has direct, quantifiable impact on revenue, deliverability, and customer experience. The right approach shapes not just messaging volume and platform cost, but also ensures intent-based targeting and operational efficiency at scale.

How Klaviyo Defines and Tracks Added to Cart vs. Checkout Started Events

Klaviyo distinguishes Added to Cart from Checkout Started events by monitoring specific customer actions on the storefront. The Shopify-Klaviyo integration captures these through dedicated JavaScript snippets or API calls, enabling the events to populate analytics, customer timelines, and automation triggers. The Added to Cart event fires when a product is placed in the shopping cart, triggering Klaviyo's Track API if the correct snippet is installed. The payload includes fields such as product_id, variant_id, collection_id, product_name, price, quantity, cart_value, and timestamp. Some Shopify themes or headless builds do not include this snippet by default, requiring manual implementation to ensure event capture (Klaviyo documentation).

The Checkout Started or Started Checkout event is triggered when a buyer enters their email and advances from cart to the checkout process. Its API event includes checkout_url, cart_value, email, an itemized array, address fields as available, and a timestamp (Shopify data reference). Unlike Added to Cart, Checkout Started is tightly bound to buyer identity since a valid email must be submitted, making it a stronger signal of purchase intent. Both events appear in Klaviyo's Analytics > Metrics dashboard with detailed filtering and in each customer's profile timeline.

Deduplication in Klaviyo operates at the event ID or cart token level to avoid repeated triggers for the same event within a short interval. For Checkout Started, deduplication is strict due to Shopify's unique checkout token. Added to Cart is deduplicated less strictly; rapid adds or implementation errors can yield excess events. Flow filters can further refine which actions trigger automations by evaluating fields such as product_id or cart_value (Flow trigger reference). Merchants should frequently audit event volumes and trigger counts in the Analytics > Metrics screen and resolve any mapping or drop-off issues to ensure the integrity of buyer intent signals.

Intent Depth: Benchmarking Buyer Readiness in Each Trigger

Checkout Started events consistently identify buyers with a higher likelihood of completing a purchase, as advancing past the cart demands explicit engagement, including providing a contact email. Most platforms, including Shopify and WooCommerce, mark Checkout Started only after the buyer moves beyond the cart and submits identifying information (Shopify reference). Added to Cart, in contrast, is generated by any cart interaction, capturing many low-intent or fleeting sessions.

Industry-wide, 69.9%, 74% of carts are abandoned, whereas checkout abandonment falls to 17%-23%. This intent gap demonstrates why Added to Cart triggers encompass far more but far less qualified sessions, while Checkout Started reliably signals attributable, actionable buyer journeys (Klaviyo abandoned cart guide). Flows targeting Checkout Started drive much higher engagement: open rates outperform Added to Cart flows by 8%-15%, and revenue per send achieves a 2x, 5x lift. Checkout Started conversion rates commonly fall between 8%-12%, contrasting with the 2%-3% typical of Added to Cart triggers (Trigger filter documentation).

Critically, the broad net of Added to Cart increases send count but introduces contact noise, diluting performance. Checkout Started mandates email capture at trigger, tightly linking flows to real identities and future segmentation. For operators, transitioning from cart to checkout-based automation reduces send volume by 65%-80%, boosting attributed revenue and improving marketing unit economics. The result is cleaner, more targeted lifecycles and actionable segmentation within Klaviyo (Event data usage).

Double-Send and Messaging Overlap: Where the Failure Mode Costs You

If both Added to Cart and Checkout Started flows are active without robust mutual exclusivity filtering, the same customer will receive duplicative reminders from both flows about a single session. For example, a user adds to cart, firing Flow 1, then starts checkout and submits email, firing Flow 2. Both flows trigger by default unless filters block redundant sends (Abandoned cart flow guide).

Best practices dictate adding filter logic such as Has Started Checkout zero times since Added to Cart to the Added to Cart flow, and Has Placed Order zero times since Started Checkout to the Checkout Started flow, referencing each event's timestamp to ensure recency (Flow filter usage). Without these, send volume can double, inflating cost and heightening list fatigue. Industry benchmarks indicate that complaint rates can rise to 0.2%-0.5% per recipient when redundant flows overlap, far above the 0.1% spam threshold monitored by most email service providers (ESPs' guidance on complaints). This undermines domain-wide deliverability and suppresses future engagement.

Operators must implement these filters to prevent superfluous sends and the associated commercial and reputational risk. Audit flows regularly for overlapping sends and enforce mutually exclusive messaging by event tier.

Cost Considerations: Messaging Volume, Platform Pricing, and Marginal Returns

Trigger choice drives Klaviyo billing via its per-contact and per-email pricing model. Every unique contact messaged is an active profile for billing purposes, and platform costs rise in line with email send count. Added to Cart flows, triggering on broader activity, capture more contacts, especially heavy browsers, and multiply sends per session. If a store logs 10,000 Added to Cart but only 1,500 Checkout Started events weekly, send and contact billing diverge sharply. Each incremental message exposes accounts to higher tiers and increased risk of unsubscribes and spam flags.

• Contacts Messaged: Early-funnel triggers substantially increase billed contact count.
• Emails Sent: Message count grows with Added to Cart, compounding total platform outlay.

Klaviyo's prebuilt flows default to Checkout Started to keep deliverability, cost, and ROI in balance, recommending broader triggers only with strict suppression and filtering criteria in place (Klaviyo help). On high-traffic stores, early-trigger flows risk ballooned expense, with diminishing marginal conversion returns (Event data personalization). Platform reports within Analytics > Campaign Performance and Flows > Flow Performance highlight how scaling triggers changes flow economics and CPA.

*Event volume ratios are referenced from Klaviyo flow documentation and order-of-magnitude operator data (Documentation).

As flows widen, review the Account > Billing dashboard for the impact on both 'Active Profiles' and 'Emails Sent' to project step increases in COGS.

How to Decide: Practical Criteria for Choosing a Trigger in Your Account

To select the optimal trigger, start by auditing current flow performance in Klaviyo. Navigate to Analytics, then Flows > Triggered Emails Sent, and compare Added to Cart versus Checkout Started event volumes and conversion performance. Examine cart_value, Cart Items, and Email fields to ensure consistency and verify that flows align with high-intent signals (Flow triggers and filters).

If Added to Cart volume is double Checkout Started and conversion rates are low, prioritize Checkout Started as the flow trigger. This ensures email is always captured, tying messaging to known identities (Shopify data reference). Monitor suppression and complaint rates in cases of frequent unsubscribes or spam flags, often indicative of high-volume, low-intent triggers. Review Flow Analytics for overlapping sends; use trigger filters to enforce exclusivity between flows.

Vertical exceptions do exist. In high-consideration or luxury verticals where prospects research extensively or revisit carts over time, Added to Cart triggers, with additional filter constraints, can remain appropriate. Verticals where cart reuse spans sessions, such as groceries or auto parts, may also justify layered flows, provided filtering is meticulously managed (Abandoned cart flow guide).

Default recommendation: deploy Checkout Started as the primary abandoned cart flow trigger. Supplement with Added to Cart only once you design robust intent validation and suppression logic based on fields such as cart_value or minimum item count (Flow filters reference).

• Use Analytics > Flow Performance to check for double-sends.
• Edit flow settings to enforce time-based cross-flow suppression.
• Audit Profile Activity Feeds for rapid trigger-fire patterns and adjust flow timing accordingly.

Trigger and flow selection should be regularly audited and refined within Analytics > Flows > Triggered Emails Sent based on evolving site traffic and conversion metrics (Event data best practice).

Advanced: Custom Event Strategies and Alternative Triggers

For organizations with engineering capacity, it's possible to instrument more precise custom events using Klaviyo's API. These may include triggers based on checkout dwell time, cart revisits, or interaction scoring levels, delivering messages only when a customer has demonstrated substantial intent beyond default triggers.

To implement, extend your ecommerce integration to push events via the /api/v1/event endpoint or update the front-end tracking snippet. Custom events, such as "Expressed Checkout Intent", can reference behaviors like revisiting a cart, submitting a discount code, or a long checkout dwell, with property-level filtering within Klaviyo flows (Event data personalization). Flows set to these metrics unlock segment exclusion by property value (e.g., cart value, item type), which is not possible on a contact-profile basis for event-triggered flows (Trigger filters explanation).

Maintenance burden rises with custom tracking schemes: custom events require quality assurance as site features evolve, and reporting accuracy must be validated within Analytics > Flow Performance Report. Compared to the operational stability of standard Checkout Started triggers, guaranteed to fire on every major ecommerce platform when a shopper submits their checkout email, custom event approaches demand active oversight (Shopify/Klaviyo integration reference).

For high-SKU or complex catalogs, or where consumer intent is hard to infer, custom triggers can reduce abandoned cart email volume by up to 20%-30%, sharply focusing messaging on true prospects (Abandoned cart customization). Simpler setups or organizations with limited engineering resources remain best served by Checkout Started, which combines accuracy, reliability, and minimal maintenance overhead.

Custom event strategies are powerful but must be commercially justified; overengineering adds risk and complexity unnecessarily. Flow design should remain responsive to campaign and funnel analytics, adapting as buyer behavior and platform integration evolves.

Sources

• Understanding flow triggers and filters | Klaviyo Help Center
• How to create an abandoned cart flow | Klaviyo Help Center
• Shopify data reference | Klaviyo Help Center
• WooCommerce data reference | Klaviyo Help Center
• How to use event data to personalize email and SMS flows | Klaviyo Help Center