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.

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.
  
  

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:

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.

Source: Klaviyo 

2. Use Klaviyo’s Profile Merge Tool

• Within the UI, navigate to a profile → Profile actions → Merge profile. Type the other profile’s email or name, pick which to keep (destination) and which to merge (source). Merging is permanent; the source’s events and list memberships integrate into the kept profile. 

Source: Klaviyo 

3. Standardise Identifiers at Signup

• Prevent mess before it starts. At capture points, require both email and phone, and format your phone numbers using E.164 standard (e.g. +44). This ensures fewer mismatches later. Also leverage Klaviyo’s identity resolution transformations (in Advanced KDP) to merge typos or alias emails under overlapping identifiers.

Source: Klaviyo 

4. Correct External ID Mapping

• Make sure your Shopify, WooCommerce, or other systems pass clean, consistent external IDs (customer IDs) to Klaviyo. If one system sends inconsistent or missing external IDs, you’ll see ghost duplicates. Monitor your sync logs for any discrepancies.

5. Clean Imported Data

Before uploading lists or CSVs:

• Remove exact duplicates.

• Strip test/fake emails (e.g. test@example.com).

• Confirm phone formatting with country codes.

Klaviyo performs auto-deduplication on imports when identifiers match exactly—but only exact matches. Non-exact ones must be caught manually.

6. Prevent Duplicates with the API

• 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.

• Code snippet example:

• Caution: merges are irreversible, so test on staging.

7. QA High-Value Flows After Merging

• After a merge, reevaluate high-impact flows (abandoned cart, browse, post-purchase). Ensure the merged profile correctly enters, exits, or continues in flows according to your filters. Also re-run key segments like “2+ purchases” to confirm person-level logic holds.

8. Troubleshoot Identity Errors

• If duplicates don’t merge, check for formatting inconsistencies (e.g. spaces, country codes). If flows misfire, verify that the merged profile holds all required custom properties or tags used in filters. Also check that Klaviyo.js or tracking code is loading properly to capture identifiers.

9. Track Data Quality with Predictive Analytics

• Use Klaviyo’s CLV, churn-risk, and cohort dashboards to spot anomalous behavior. Profiles with erratic or weak signals may indicate duplication issues. Clean duplicates before they degrade your predictive models.

• See our guide on predictive analytics.

Privacy Note: All merges must respect GDPR/CCPA — consent (opt-in/out) always transfers with profiles.

Advanced Klaviyo Identity Resolution Use Cases

Identity resolution goes beyond duplicate cleanup — it enables smarter cross-channel marketing and compliance.

Key Use Cases

• Cross-channel matching: Extended ID bridges anonymous → known journeys across email, SMS, and ads. This improves GA4 attribution and remarketing alignment. See our Google Analytics integration guide.

• Multi-brand hygiene: For multi-store setups, enforce consistent identifiers across brands to prevent merge conflicts.

• Consent handling: Per GDPR/CCPA, consent must remain intact post-merge. Klaviyo ensures SMS/email opt-ins are preserved (SMS compliance guide).

• Anonymous-to-known journeys: Klaviyo’s Extended ID ensures continuity when a customer browses anonymously and later signs up.
  
  

The ROI Benefits of Clean Identity Resolution in Klaviyo

Fixing duplicate profiles isn’t just about tidying your database — it directly impacts revenue. When profiles are fragmented, customers slip through cracks: abandoned cart emails never send, segments misfire, and reporting underestimates ROI. With clean identity resolution, your marketing works the way it’s supposed to.

ROI Benefits

• Segmentation accuracy: Clean RFM scoring drives stronger campaign ROI. See our segmentation strategies blog.

• Cleaner attribution: GA4 and Klaviyo attribution models connect campaigns to correct conversions (Klaviyo UTM Tracking guide).

• Improved personalisation: Unified profiles allow product blocks and flows to reflect full history (Klaviyo Product Block blog).

• Lower support costs: Fewer duplicate accounts reduce tickets and confusion.

Klaviyo case studies show brands can unlock a 10–20% uplift in repeat purchases and a 15% boost in campaign CTRs after implementing systematic deduplication.

Quick Klaviyo Identity Resolution Checklist

Keeping your database clean isn’t a one-time task — it requires steady upkeep. A simple routine ensures your data remains reliable as you scale.

5-Step Checklist

1. Audit monthly: Export profiles and search for duplicates.

2. Enforce identifiers: Capture both email + formatted phone (E.164).

3. Sync integrations: Confirm Shopify/WooCommerce pass consistent IDs.

4. Test flows: QA abandoned cart and post-purchase journeys after merges.

5. Monitor predictive analytics: Use CLV and churn dashboards to catch anomalies.

Pro Tip: Document your identifier rules (email required, phone formatting, external ID mapping) and review them quarterly to keep your data governance tight.

FAQs

1. Does Klaviyo merge profiles automatically?

• Yes, but only when identifiers like email or phone match. It never merges based on names or inferred matches.

2. Can I un-merge a profile?

• No. Merges are permanent. Always test before API merges.

3. Does consent transfer during a merge?

•  Yes. Klaviyo preserves opt-in/out status for both email and SMS during merges.

4. How do I confirm if flows work post-merge?

• Check the Activity Feed for merge events, then test flows like abandoned cart and post-purchase.

5. Will duplicate profiles affect predictive analytics?

• Yes — duplicates dilute CLV, churn-risk, and cohort analysis. Clean profiles restore model accuracy.

Conclusion

Duplicate profiles don’t just clutter your database — they cost you money. Broken flows, messy segments, and skewed reports all chip away at ROI.

Klaviyo’s identity resolution gives you a single, reliable view of each customer. With clean data, your marketing becomes sharper, your reporting more credible, and your customer experience seamless.

For growing brands, this isn’t optional. Clean profiles are the foundation of profitable growth — and the key to unlocking smarter personalisation, stronger attribution, and repeat sales that scale.

Key Takeaways

• Identity Resolution Defined: Deterministic matching across email, phone, and external IDs.

• 9 Fixes to Apply: From auditing and merges to API and import hygiene.

• Advanced Use Cases: Consent handling, multi-brand hygiene, and Extended ID.

• ROI Impact: Up to 20% uplift in repeat purchases and higher CTRs.

• Maintenance Checklist: Audit monthly, enforce identifiers, test flows, and monitor analytics.
  
  
  

Are duplicate profiles dragging down your campaign ROI?

Unify fragmented customer data and restore flow performance with a free Klaviyo identity resolution audit. Our experts will pinpoint merge issues and help you fix them fast. Click here to schedule your free audit now.