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Metrics type: Cross-Platform Metrics • Category: Email Marketing
% of paying customers actually on the email list. Below 60% means checkout opt-in is broken or the E-Commerce store sync is stale.

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At a glance

The percentage of paying customers (from connected commerce platform) who appear as subscribed in any Mailchimp audience. Computed as COUNT(distinct customer emails subscribed in Mailchimp) ÷ COUNT(distinct customer emails on commerce platform) × 100. Below 60% means checkout opt-in is broken, the Mailchimp Stores sync is stale, or customers are aggressively opting out at checkout. Below 40% indicates a structural acquisition gap that no amount of campaign optimisation can close.

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Calculation

Calculated automatically from your Mailchimp data. See the At a glance summary above for what the metric tracks and the worked example below for a typical reading.

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Worked example

A small DTC sustainable-skincare brand on Shopify, Mailchimp Standard. Snapshot taken 02 May 26. Five observations:
  1. At 53.3%, the merchant is below the alert threshold. Roughly 8,600 paying customers are unreachable via email; that’s the cost of the acquisition leak. Average customer lifetime value is £85, so the unreachable cohort represents ~£730k of email-recoverable revenue opportunity over time. This is a structural problem, not a content problem.
  2. The most common cause is the checkout opt-in default state. If the “Email me with news and offers” checkbox is unchecked-by-default at Shopify checkout, capture rate is typically 20-40%. Checked-by-default lifts to 60-75% (legal in UK/US for marketing email under existing-customer relationship; not legal in EU under GDPR). Pre-purchase popup capture lifts further to 80-90%. Audit the checkout opt-in setting first.
  3. Mailchimp Stores sync may also be stale. If Shopify has 18,400 customers but Mailchimp’s e-commerce contact sync hasn’t run recently, recent customers are absent from Mailchimp. Audit MC03 catches this. Open Mailchimp → Integrations → Shopify → check “Last sync” timestamp. If >24h old, manually re-sync.
  4. A 73% coverage merchant turning on a pre-purchase popup typically lifts to 88-92% within 90 days. This pattern is well-tested. The 73% baseline represents customers who voluntarily opted in at checkout; the additional 15-19 pp comes from pre-purchase incentivised signups (10% off first order in exchange for email). Coverage compounds over months as new customers opt in via popup.
  5. Coverage above 100% is possible but indicates the audience is contaminated. Merchants who buy email lists, run lead-generation popups without verifying email validity, or have stale customer data can show 110-130% coverage. This is bad: the extra subscribers are non-customers, often fake addresses, and damage deliverability when sent to. Coverage should asymptote near 95%, not above.

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Sibling cards merchants should reference together

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Reconciling against the vendor’s own dashboard

Where to look in Mailchimp’s own dashboard: Mailchimp does not surface this ratio natively. The closest views are Mailchimp → Audience → All Contacts for the subscribed-contact count (numerator candidate) and Mailchimp → Integrations → Shopify → Sync status showing the e-commerce contact sync. This card is a Vortex IQ-derived ratio; no single Mailchimp screen shows it. For the denominator, refer to your commerce platform’s customer-list endpoint. Shopify: Customers count in admin. BigCommerce: similar. Adobe Commerce: Customers → All Customers. Why our number may legitimately differ from a hand-built calculation: Cross-connector reconciliation (this is the central purpose):

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Known limitations / merchant FAQs

My coverage is 45%, what should I do first? Three diagnostic steps in order: (1) check the Mailchimp Stores integration sync status, audit MC03 catches stale syncs; (2) audit the Shopify checkout opt-in setting, is the email-marketing checkbox checked-by-default? if not, that’s typically 25-40 pp of the gap; (3) look at customer acquisition channels, customers acquired via paid ads tend to opt in less than organic-search customers because they’re cold, less engaged, and treat the purchase as transactional. What’s a healthy coverage figure? For DTC consumer brands: 60-80% is healthy, 80-95% is exceptional (usually requires a pre-purchase popup with incentive). For B2B: 75-95% is healthy because B2B buyers expect ongoing communication. For one-time-purchase categories (wedding, gifts): 30-60% is normal because customers don’t expect ongoing email. Why is Klaviyo’s coverage figure higher than Mailchimp’s on the same store? Klaviyo retains anonymous browser-only profiles (no email consent) which are typically 30-50% larger than the consented-subscriber count. If the Klaviyo card is using the broader profile count, it shows higher coverage. The honest comparison is “active consented subscribers”, which usually matches Mailchimp’s number to within 5 pp. Coverage above 100%, is that an error? Probably not an error, but a warning. Coverage >100% means more email subscribers than commerce-platform customers. Common causes: (a) lead-magnet popups that capture emails from non-buyers (healthy if those emails are real); (b) purchased / rented email lists (unhealthy, deliverability risk); (c) imported subscribers from a previous system (healthy if recent and double-opt-in confirmed). Coverage >120% sustained is a deliverability risk, audit list source. Does this card account for guest checkouts? Guest checkouts that include the customer’s email count toward the denominator (customer count). If they opted in to marketing during checkout, they count toward the numerator too. Guest checkouts that don’t capture email at all aren’t visible to either side, they don’t appear here. My coverage dropped 10 pp in 30 days, what happened? Three usual causes: (a) you ran a list cleanse that removed dormant subscribers (numerator dropped); (b) you ran a promotion that brought in many new customers, most of whom didn’t opt in (denominator grew faster than numerator); (c) Mailchimp Stores sync broke and new customers stopped syncing (numerator stalled). Audit MC03 distinguishes (c) from (a) and (b). Should I include unsubscribed customers in the denominator? Strictly, no. Unsubscribed customers are still customers but can’t receive marketing email. The denominator here is “all customers”; coverage tells you “of all customers, what fraction can I email today”. Some merchants prefer “of all customers, what fraction ever opted in”, which is a different (always-higher) metric. Why is the today value volatile? Coverage is point-in-time. Both numerator and denominator move continuously: customers opt out, new customers buy. For most accounts the figure is stable to within ±0.5 pp day-to-day. Big swings (>2 pp) usually indicate sync problems or a list-cleanse event. Can I exclude inactive customers (no purchase in 12+ months)? Not directly from this card. The denominator includes all-time customers, including ones who haven’t bought recently. To exclude them, look at Shopify’s “Active customers” segment definition and re-compute manually. For most coverage decisions, the all-time view is the right one (you want to email past customers to win them back). Which audience does the numerator pull from? Every audience in the account. A customer subscribed to ANY audience counts. This means a B2B trade list and a consumer list can both contribute. Per-audience coverage isn’t surfaced here; if your audiences serve different segments and you want per-audience coverage, build a Mailchimp segment per audience and check the per-segment count manually.

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Tracked live in Vortex IQ Nerve Centre

Audience Coverage of Customer Base is one of hundreds of KPI pulses Vortex IQ tracks across Mailchimp and 70+ other ecommerce connectors. Nerve Centre runs the detection layer; Vortex Mind investigates the cause when something moves; Ask Viq lets you interrogate any number in plain English. Start for free or book a demo to see this metric running on your own data.