> ## 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: Retention Marketing Efficiency

> Track your returning customer marketing efficiency ratio. Understand what percentage of repeat buyer revenue is spent on advertising.

<Tip>
  Returning Customer MER measures what percentage of your returning customer order revenue is spent on advertising. This is a key metric for understanding retention marketing efficiency.
</Tip>

## Formula

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

### Formula Components

| Metric                                                                                               | Definition                                                |
| ---------------------------------------------------------------------------------------------------- | --------------------------------------------------------- |
| **Total Ad Spend**                                                                                   | Combined advertising spend across all connected platforms |
| [**Returning Customer Revenue**](/reference/metrics/orders/revenue/returning-customer-total-revenue) | Total revenue from repeat buyer orders                    |

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

***

## Example

Your Shopify store generated **\$120,000** in returning customer revenue while spending **\$40,000** on advertising.

| Metric                     | Value     | Calculation                  |
| -------------------------- | --------- | ---------------------------- |
| Total Ad Spend             | \$40,000  | All ad platforms             |
| Returning Customer Revenue | \$120,000 | Repeat buyers                |
| RC MER                     | 33.3%     | (\$40,000 ÷ \$120,000) × 100 |

A RC MER of 33.3% means you spend \$0.33 on advertising for every \$1 of returning customer revenue.

***

## How It Works

RC MER isolates marketing efficiency for customer retention. Since returning customers are typically cheaper to convert than new customers, RC MER is usually lower than NC MER. The difference reveals how much value your existing customer base adds to blended efficiency.

***

## When to Use

| Scenario                         | Action                                         |
| -------------------------------- | ---------------------------------------------- |
| Retention marketing evaluation   | Measure remarketing efficiency                 |
| Budget allocation decisions      | Compare RC MER to NC MER for optimal split     |
| Loyalty program ROI              | Understand cost to generate repeat purchases   |
| Identifying retention efficiency | Lower RC MER indicates strong customer loyalty |

***

## Related Metrics

| Metric                                                                               | Relationship                           |
| ------------------------------------------------------------------------------------ | -------------------------------------- |
| [MER](/reference/metrics/orders/performance/total-mer)                               | Total MER including all customers      |
| [RC MER (Gross)](/reference/metrics/orders/performance/returning-customer-gross-mer) | RC MER using gross revenue             |
| [RC MER (Net)](/reference/metrics/orders/performance/returning-customer-net-mer)     | RC MER using net revenue               |
| [NC MER](/reference/metrics/orders/performance/new-customer-total-mer)               | Marketing efficiency for new customers |

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