> ## 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.

# Cost per Login: Measure Login Acquisition Efficiency

> Track cost per login to measure how efficiently your ads drive authenticated engagement. Calculate average ad spend per login event for your Shopify store.

<Tip>
  Cost per Login measures the average ad spend required to generate one login event on your site.
</Tip>

## Formula

<Info>
  **Cost per Login** = **Channel Spend** ÷ **Logins**
</Info>

### Formula Components

| Metric                                                                    | Definition                                      |
| ------------------------------------------------------------------------- | ----------------------------------------------- |
| [**Channel Spend**](/reference/metrics/advertising/blended/blended-spend) | Total advertising spend across channels         |
| [**Logins**](/reference/metrics/funnel/engagement/login)                  | Total login events tracked by the Upstack pixel |

| Metadata        |                         |
| --------------- | ----------------------- |
| **Type**        | Currency                |
| **Data Source** | [Upstack Pixel](/pixel) |
| **Aggregation** | Ratio                   |

***

## Example

Your store spent **\$5,000** on ads in January and tracked **2,500** login events.

| Metric             | Value      | Calculation        |
| ------------------ | ---------- | ------------------ |
| Channel Spend      | \$5,000    | Total ad spend     |
| Logins             | 2,500      | Total login events |
| **Cost per Login** | **\$2.00** | \$5,000 ÷ 2,500    |

***

## How It Works

The Upstack pixel captures login events when visitors authenticate on your site. Cost per Login divides your total ad spend by the number of login events, showing how efficiently your ads drive authenticated engagement. Lower values indicate more cost-effective campaigns at re-engaging existing customers.

***

## When to Use

| Scenario                         | Action                                                               |
| -------------------------------- | -------------------------------------------------------------------- |
| Evaluating retention campaigns   | Compare Cost per Login across campaigns targeting existing customers |
| Measuring loyalty program ROI    | Track if loyalty-focused ads drive efficient re-engagement           |
| Assessing remarketing efficiency | Monitor cost to bring customers back to authenticate                 |
| Identifying high-value audiences | Find segments with lower Cost per Login for optimization             |

***

## Related Metrics

| Metric                                                                    | Relationship                                         |
| ------------------------------------------------------------------------- | ---------------------------------------------------- |
| [Logins](/reference/metrics/funnel/engagement/login)                      | The denominator in this calculation                  |
| [Login Value](/reference/metrics/funnel/engagement/login-value)           | Total value attributed to login events               |
| [Cost per Sign Up](/reference/metrics/funnel/engagement/cost-per-sign-up) | Similar cost efficiency metric for new registrations |

[See all Engagement metrics →](/reference/metrics/funnel/engagement)