Duplicate profiles in Klaviyo don’t just clutter your database — they break segments, confuse flows, and waste marketing spend. A customer with two profiles might get skipped in a win-back flow or miscounted in predictive analytics, costing you conversions.
Klaviyo’s identity resolution merges data from multiple touchpoints into a single source of truth, but this only works if you understand how identifiers and merge rules function. Clean, unified data unlocks accurate personalisation, reliable attribution, and a stronger ROI.
What This Guide Covers
- How Klaviyo identity resolution works
- Key identifiers and merge rules
- 9 ways to prevent and fix duplicates
- Troubleshooting common sync errors
- The ROI impact of clean profiles
What is Klaviyo Identity Resolution?
Klaviyo identity resolution is the process of merging fragmented customer data into one profile. Anytime a customer interacts — signing up with a new email, checking out with a different phone, or browsing anonymously — Klaviyo attempts to unify these into a single record. According to the Klaviyo Help Center, identity resolution ensures every marketing action is tied to the correct person.
Why It Matters
Prevents flow errors: Abandoned cart and browse flows won’t trigger if the cart is tied to a duplicate. See our Klaviyo Abandoned Checkout Flow guide.
Improves segmentation: Predictive analytics and RFM segmentation rely on clean, unified data.
Strengthens attribution: Clean IDs ensure correct ROI reporting in GA4 and Klaviyo dashboards.
Enables personalisation: You can pull full order and engagement history into one journey.
How Klaviyo Identity Resolution Works Behind the Scenes
Identity resolution in Klaviyo is deterministic, meaning profiles merge only when key identifiers overlap. This protects against accidental merges while still consolidating data across devices and channels.
Key Identifiers That Merge Profiles
Email address: The primary identifier in Klaviyo. When someone submits a form, places an order, or clicks an email, Klaviyo uses the email to link and merge profiles.
Phone number: Required for SMS marketing and must follow E.164 format. If a phone-only profile later gets an email, Klaviyo merges them into one record
Profile ID: A unique 26-character identifier assigned to every Klaviyo profile, visible in the profile URL. It ensures each customer record is distinct and traceable. Some older profiles may have a six-character ID, which is still valid and unique.
klaviyo Profile ID – New.png Alt text: Klaviyo profile page URL showing a new profile ID highlighted in the browser address bar.
klaviyo Profile ID – Older.png Alt text: Klaviyo profile page URL showing an older profile ID highlighted in the browser address bar.
Source: Klaviyo
External IDs: IDs from connected platforms like Shopify or WooCommerce. Klaviyo uses these for mapping, but stresses they must remain unique to avoid duplication
Anonymous IDs: Generated when someone browses without identifying (via Klaviyo.js or pixels). Once they provide an email or phone number, their anonymous activity merges into their known profile.
Extended ID: Klaviyo’s first-party cookie enabling up to one year of anonymous-to-known continuity across devices. This improves attribution and remarketing by connecting browsing sessions to the eventual customer profile.
Klaviyo Data Settings.png Alt text: Klaviyo Data Preferences settings page with options for anonymous visitor tracking, Shopify tracking, and Extended ID.
Source: Klaviyo
Customer Identification Triggers
Onsite JavaScript snippet and Shopify Server Pixel
Form submissions (email/phone capture)
Message click-through events
Checkout and account creation
9 Proven Ways to Fix Duplicate Profiles and Boost ROI
Cleaning duplicates requires both proactive prevention and reactive fixes. Here are nine verified methods, aligned with Klaviyo’s documentation:
Proven Ways to Fix Duplicate Profiles – table.png Alt text: Table listing fixes for duplicate profiles with descriptions and tools, including API merge and predictive analytics.
1. Audit Your Database Regularly
Start by exporting profiles grouped by email + phone, then scan for duplicates. In each profile’s Activity Feed, look for Merge profile events to see past consolidations. This helps you validate which merges went correctly and which still need manual cleanup.
Klaviyo provides a Profile Merge API endpoint for programmatic merging. You pass a source profile to merge into a destination. The endpoint runs asynchronously, moving events and deleting the source.