> ## 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 (Net Sales): Retention Net Efficiency

> Track returning customer marketing efficiency using net sales. Understand what percentage of repeat buyer net revenue is spent on ads.

<Tip>
  Returning Customer MER (Net) measures what percentage of your returning customer net sales (after discounts and refunds) is spent on advertising.
</Tip>

## Formula

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

### Formula Components

| Metric                                                                                 | Definition                                                       |
| -------------------------------------------------------------------------------------- | ---------------------------------------------------------------- |
| **Total Ad Spend**                                                                     | Combined advertising spend across all connected platforms        |
| [**RC Net Revenue**](/reference/metrics/orders/revenue/returning-customer-net-revenue) | Net order sales from returning customers after discounts/refunds |

| 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 **\$110,000** in returning customer net sales while spending **\$40,000** on advertising.

| Metric         | Value     | Calculation                  |
| -------------- | --------- | ---------------------------- |
| Total Ad Spend | \$40,000  | All ad platforms             |
| RC Net Sales   | \$110,000 | After discounts/refunds      |
| RC MER (Net)   | 36.4%     | (\$40,000 ÷ \$110,000) × 100 |

A RC Net MER of 36.4% means you spend \$0.36 on advertising for every \$1 of returning customer net sales actually collected.

***

## How It Works

RC Net MER uses returning customer net sales as the revenue base, accounting for loyalty discounts and refunds. This gives you the most accurate view of retention efficiency relative to revenue actually kept from repeat customers.

***

## When to Use

| Scenario                          | Action                                    |
| --------------------------------- | ----------------------------------------- |
| True retention cost analysis      | Include discount and refund impact        |
| Heavy loyalty discount strategies | See real MER after promo impact           |
| High repeat customer refund rates | Understand true marketing cost            |
| Setting retention budget limits   | Ensure RC MER allows for positive margins |

***

## Related Metrics

| Metric                                                                               | Relationship                        |
| ------------------------------------------------------------------------------------ | ----------------------------------- |
| [RC MER](/reference/metrics/orders/performance/returning-customer-total-mer)         | RC MER using total revenue          |
| [RC MER (Gross)](/reference/metrics/orders/performance/returning-customer-gross-mer) | RC MER using gross revenue          |
| [MER (Net)](/reference/metrics/orders/performance/net-mer)                           | Net MER for all customers           |
| [RC Net Revenue](/reference/metrics/orders/revenue/returning-customer-net-revenue)   | The denominator in this calculation |

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