How to Build Custom Metrics
Build the KPIs your business runs on — combine Fospha, Last-Click, and Ad Platform data in a single formula, without leaving the platform.
What are Custom Metrics?
Custom Metrics let you define your own performance indicators using a formula builder inside Fospha. Once created, a custom metric works like any native metric — you can add it as a column in your reporting table, include it in Saved Views, export it alongside your other data, and query it through Ask Fospha AI.
The builder supports three types of inputs: standard Fospha data fields, Fospha's pre-calculated metrics (such as ROAS and CAC), and fields from Last-Click attribution and your ad platforms. This means you can build both business-specific KPIs and cross-model comparisons inside Fospha, rather than reconstructing them in a spreadsheet.
How to create a Custom Metric
Step 1 — Go to the Custom Metrics builder
Navigate to Settings in the left-hand menu and select Custom Metrics. Click Create metric.
Step 2 — Name your metric
Give your metric a name that will make sense to everyone who uses it. This is how it will appear in column headers, Saved Views, and exports. You can also add an optional description — useful for documenting what the formula is doing for teammates who didn't build it.
Step 3 — Build your formula
Click into the formula field. Type or select the fields you want to use. Use the following operators to combine them:
+to add-to subtract×to multiply÷to divide( )parentheses to control the order of operations
The builder validates your formula as you type and surfaces any errors in plain English before you save — so you can fix issues before the metric is live.
Step 4 — Save
Click Save. Your metric is now available across Reporting, Saved Views, and Exports.
What you can use as inputs
Standard Fospha fields
These are the raw data fields that underpin Fospha's measurement.
- Revenue
- Cost / Spend
- Conversions
- New Conversions
- Impressions
- Clicks
- Visits
- New Revenue
Fospha computed metrics
These are Fospha's pre-calculated KPIs, available as direct inputs. Rather than reconstructing a metric like ROAS from its underlying fields, you can select it directly and use it in a ratio or efficiency formula.
- ROAS
- New Customer ROAS
- CAC
- CPP
- CVR
- AOV
- New Customer AOV
- Engaged Sessions
- Subscription Conversions (only visible if subscription data is connected)
- Subscription Revenue (only visible if subscription data is connected)
Last-Click and Ad Platform fields
These expose the raw performance data from Last-Click attribution and your ad platforms as selectable inputs.
The same set of fields is available for both Last-Click and Ad Platform:
- Visits
- Clicks
- Cost
- Impressions
- Conversions
- New Conversions
- Revenue
- New Revenue
This is what makes cross-model comparison possible inside Fospha. You can build a formula that puts Fospha-attributed values alongside Last-Click or Ad Platform values in a single number, without exporting to a spreadsheet.
Example formulas
Using standard fields and computed metrics
| Metric name | Formula | What it shows |
|---|---|---|
| CAC Payback Multiplier | AOV ÷ CAC | How quickly the average order value covers the cost of acquiring that customer |
| New Customer Efficiency Ratio | New Customer ROAS ÷ ROAS | Whether growth is coming from genuinely new customers or repeat purchasers — a ratio above 1 means new-customer performance is stronger than blended |
| Blended Cost of Sale | Cost ÷ Revenue | Your overall cost as a percentage of attributed revenue |
Using Last-Click and Ad Platform fields
| Metric name | Formula | What it shows |
|---|---|---|
| Last-Click Cost of Sale | Cost ÷ Last-Click Revenue | A Last-Click COS built natively in the platform, comparable against your Fospha COS in the same column |
| Engaged Conversion Rate | Conversions ÷ Engaged Sessions | Ties Fospha-attributed conversions to site engagement |
| Cross-model ROAS delta | ROAS ÷ Last-Click ROAS | Direct ratio of Fospha ROAS to Last-Click ROAS — above 1 means Fospha is attributing more value; below 1 means Last-Click is attributing more |
| Ad Platform Efficiency Index | ROAS ÷ Ad Platform ROAS | Shows how Fospha's measurement compares to your ad platform's own reported ROAS |
A note on mixing fields across models
There is no restriction in the builder on combining fields from different attribution models in a single formula — for example, Last-Click Cost ÷ Ad Platform Revenue is technically buildable. Apply your own judgement on whether a mixed-model ratio produces a number that is analytically meaningful for your use case.
Tips
Name metrics clearly. A name like "LC COS" is clear to you now but may confuse a colleague or agency partner opening the platform for the first time. "Last-Click Cost of Sale" takes two seconds longer to type and saves a conversation later.
Use parentheses for anything beyond a simple ratio. The builder follows standard order of operations, but if your formula has more than two steps, parentheses make the intended calculation explicit and avoid errors.
Build once, share everywhere. Custom Metrics are account-level — any metric you create is available to all users in your organisation without them needing to rebuild it themselves.
Check your plan for computed metrics. If you can't see ROAS, CAC, or AOV as selectable inputs, your plan may not include computed metrics. Speak to your Customer Success Manager to confirm access.
Troubleshooting
My formula is showing an error before I save
The builder validates formulas in real time and describes the issue in plain English. Common causes: a division where the denominator could be zero, or an incomplete formula with a hanging operator. Fix the highlighted issue and try saving again.
A colleague can't see a Custom Metric I created
Custom Metrics are available to all users in your organisation once saved. If a colleague can't see a metric, check that they have refreshed their page. If it still doesn't appear, confirm with your CSM that their account role has the correct permissions.
I can't see Custom Metrics in my dashboards
Custom Metrics is part of the Customisation Suite add-on. If the option isn't visible under 'Customize' your account may not have the add-on enabled. Contact your Customer Success Manager.