> ## Documentation Index
> Fetch the complete documentation index at: https://docs.upstackdata.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Returning Customer MER: Repeat Order Marketing Efficiency

> Track Returning Customer MER for your Shopify store. Measure marketing efficiency for repeat buyers.

<Tip>
  Returning Customer MER measures what percentage of returning customer order revenue is spent on advertising—marketing efficiency for retention.
</Tip>

## Formula

<Info>
  **RC MER** = ( **Ad Spend** ÷ **RC Order Revenue** ) × 100
</Info>

### Formula Components

| Metric                                                                                             | Definition                             |
| -------------------------------------------------------------------------------------------------- | -------------------------------------- |
| **Ad Spend**                                                                                       | Total advertising spend                |
| [**RC Total Revenue**](/reference/metrics/orders/revenue/returning-customer-total-revenue)         | Revenue from returning customer orders |
| [**customer\_type = returning\_customer**](/data-dictionary/measures-and-dimensions#customer-type) | Filters to repeat buyers               |

| Metadata        |                                                                                                                           |
| --------------- | ------------------------------------------------------------------------------------------------------------------------- |
| **Type**        | Percentage                                                                                                                |
| **Data Source** | [Shopify](/sources/catalog/shopify), [Meta Ads](/sources/catalog/facebook-ads), [Google Ads](/sources/catalog/google-ads) |
| **Aggregation** | Ratio                                                                                                                     |

***

## Example

Your store spent **\$20,000** on ads and returning customers generated **\$120,000** in revenue.

| Component  | Value     | Calculation                |
| ---------- | --------- | -------------------------- |
| Ad Spend   | \$20,000  | Total advertising          |
| RC Revenue | \$120,000 | Repeat buyer revenue       |
| **RC MER** | **16.7%** | \$20,000 ÷ \$120,000 × 100 |

***

## How It Works

RC MER shows marketing efficiency for returning customers. It's typically lower than NC MER because repeat customers don't require acquisition cost—they're already in your database. The gap between NC MER and RC MER shows the efficiency gain from retention.

***

## When to Use

| Scenario                       | Action                                        |
| ------------------------------ | --------------------------------------------- |
| Measuring retention efficiency | Track RC MER vs NC MER                        |
| Validating retention value     | Lower RC MER = more efficient repeat business |
| Budget allocation              | Shift spend toward segments with better MER   |
| LTV modeling                   | Use RC MER for lifetime value projections     |

***

## Related Metrics

| Metric                                                           | Relationship                       |
| ---------------------------------------------------------------- | ---------------------------------- |
| [MER](/reference/metrics/orders/performance/mer)                 | Overall marketing efficiency ratio |
| [NC MER](/reference/metrics/orders/performance/new-customer-mer) | MER for new customers              |
| [LTV](/reference/metrics/orders/ltv/ltv)                         | Customer lifetime value            |

[See all Performance metrics →](/reference/metrics/orders/performance)