Ecommerce dashboard: eight numbers worth a screen

Eight numbers earn one screen, and each needs its formula printed under it, because each misleads in a known way: MER, blended CAC, new-customer share, average order value, contribution margin, days to convert, unassigned share and refund rate. Shopify and GA4 document most of the ingredients, not the ratios: Shopify defines average order value as gross sales minus discounts, divided by orders, and GA4 says Unassigned is the value it uses when no channel rule matches the event data. For illustration: €10,000 of ad spend on €50,000 of net sales gives a MER of 5.0, and if 400 customers ordered, 100 of them new, blended CAC is €25 while spend per new customer is €100.

Which eight numbers belong on the screen?

Each line gives the formula, who defines it, and how it misleads:

1. MER: net sales divided by total ad spend. Shopify defines net sales as sales revenue with discounts and sales reversals factored in. MER counts every order, ads or not, so it tells you whether the business pays back its ads, not which ad did it.
2. Blended CAC: total ad spend divided by all customers who ordered, new and returning. No platform defines it, so print the formula on the screen. It looks efficient when returning customers carry the count.
3. New-customer share: new customers divided by customers. Shopify counts new customers as first-time purchasers only. A falling share beside a steady blended CAC can mean acquisition slowed while retention held the number up.
4. Average order value: gross sales minus discounts, divided by orders, excluding post-order adjustments. Refunds and exchanges do not lower it, and a few wholesale orders raise it (split them out).
5. Contribution margin: Shopify's gross profit is net sales minus cost of goods sold, and it needs costs set up in Shopify to be accurate. It comes before shipping, payment fees and ad spend, so subtract those before you call it contribution margin (calculator).
6. Days to convert: GA4's Key events attribution paths report shows days to key event, but only for users who triggered a key event, and credit stops at the lookback window. It says nothing about shoppers who never bought.
7. Unassigned share: revenue in GA4's Unassigned channel divided by total revenue. It grades your tagging, not your marketing: a jump after a campaign launch usually means a UTM problem.
8. Refund rate: Shopify reports returns and a reversed quantity rate, which is returned items divided by sold items, and GA4 processes refunds only with the order's transaction ID. Refunds arrive after the order, so read the rate by order month once the return window has passed.

What limits the GA4 half of the screen?

Two documented limits. GA4's default lookback window is 30 days for acquisition key events and 90 days for all other key events. Google also says changes to the lookback window apply going forward. For user-level data and key events data, GA4 lets you set retention to 2 months or 14 months. Google says that data for a date range longer than the retention period is not visible in Explorations. So a days-to-convert view cannot show a consideration cycle longer than the lookback window, and an exploration cannot compare with periods older than your retention.

How do you check the screen before you trust it?

1. Print the formula and its source under every number. Pass: a colleague can recompute any figure from the exports. Fail: one of them depends on a spreadsheet nobody can explain.
2. Reconcile net sales and orders for a closed month to Shopify's own report. Pass: they match, or the gap is a named item such as time zone, currency or test orders. Fail: an unexplained gap, so every ratio built on it is off.
3. List the products you sold last month that have no cost. In Shopify reports, the Inventory item cost field holds it. Pass: none. Fail: any, so contribution margin is overstated.
4. Read refund rate again after the return window. Pass: it moved little. Fail: it rose, which means the first reading flattered the month.

Sources, 30 September 2026: Analytics data points (fields) reference (Shopify Help Center, 2026); Key events attribution paths report, Select attribution settings, Data retention, Default channel group and Minimize duplicate key events with transaction IDs (Google Analytics Help, 2026).

Related answers

• Blended MER vs Platform ROAS: Which Should Drive Spend?
• New-Customer CAC (nCAC): Why Blended CAC Hides Your Real Acquisition Cost
• Reporting vs analysis: what a dashboard cannot decide
• Wholesale orders in DTC numbers: how to separate them
• Contribution margin calculator