> For the complete documentation index, see [llms.txt](https://help.modelreef.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.modelreef.io/help/drivers-variables-and-timing/modifier-drivers.md).

# Modifier Drivers

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### What is a modifier driver

Modifier drivers are series that adjust other drivers or variables. They rarely represent real world quantities by themselves.

Typical forms:

* Percentages or multipliers.
* Index values that scale a base value.
* Scenario factors that tilt another series up or down.
* Seasonality factors applied to a base trend.

Examples:

* `Driver - Modifier - Scenario Scale - Revenue`
* `Driver - Seasonality - Retail - Monthly Index`
* `Driver - Discount Factor - Customer Incentives`
* `Driver - Modifier - Cost Saving Programme`

These drivers are usually dimensionless or expressed in percentages rather than cash or unit terms.
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### Modifier drivers vs other drivers

Compared to other drivers:

* **Economic drivers** represent external conditions such as prices, FX or interest rates.
* **Operational drivers** represent internal activity such as units, headcount or utilisation.
* **Modifier drivers** represent the way you **adjust** other series to represent discounts, uplift, seasonality or scenarios.

Modifiers are layered on top of economic and operational drivers rather than standing alone.
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### Storing modifier drivers

In the Data Library, name and tag modifier drivers clearly, for example:

* Name: `Driver - Seasonality - Subscriptions - Monthly`
* Units: `Index` or `Percent`
* Tags: `Seasonality`, `Modifier`, `Scenario`

Typical values and meanings:

* 1.0 for no change.
* Above 1.0 for uplift.
* Below 1.0 for reductions.
* Or percentage values that are applied as gross up or discount rates.

Document in the notes how the modifier should be interpreted in formulas.
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\## Using modifier drivers in formulas

Examples of how modifiers can be used:

* Scenario scale
  * Formula: {% code title="Scenario scale" %}

    ```
    Revenue = BaseRevenue * ScenarioScale
    ```

    {% endcode %}
  * Where `ScenarioScale` is greater than 1 in upside scenarios and less than 1 in downside cases.
* Seasonality
  * Formula: {% code title="Seasonality" %}

    ```
    Revenue = BaseTrend * SeasonalityIndex
    ```

    {% endcode %}
  * `SeasonalityIndex` represents relative strength within a year while preserving the annual total.
* Discounts and promotions
  * Formulas: {% code title="Discounts and promotions" %}

    ```
    NetPrice = ListPrice * (1 - DiscountRate)
    COGS = BaseCOGS * CostReductionIndex
    ```

    {% endcode %}

Modifiers let you express these relationships without changing the underlying economics or operations drivers directly.
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### Scenario design with modifiers

Modifier drivers are particularly useful for scenarios because:

* You can keep base economic and operational drivers stable.
* You overlay scenario effects using modifiers.
* Modifiers can be toggled or edited without needing to touch core series.

Examples:

* `Driver - Modifier - Downside - Revenue` that gradually reduces revenue relative to base.
* `Driver - Modifier - Cost Saving Plan` that reduces certain Opex categories in transformation scenarios.
* `Driver - Modifier - Capex Deferral` that shifts some investments later in the horizon.

This keeps scenario logic explicit and easy to compare.
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### Good practice for modifier drivers

Guidelines:

* Make modifier names very clear about their purpose and scope.
* Keep base drivers and modifiers separate so you can see both the underlying plan and the adjustments.
* Use values of 1.0 as the neutral baseline when using multiplicative modifiers.
* Document how modifiers are applied, especially if multiple modifiers stack on the same variable.

Transparent modifiers make scenario conversations much easier with non modellers.
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## Related articles

* [Multi-Phase Project Cash Flows](/use-cases/capital-projects-and-infrastructure/multi-phase-project-cash-flows.md)
* [Core Modelling](/how-tos/core-modelling.md)
* [Operational Drivers](/help/drivers-variables-and-timing/operational-drivers.md)
* [Using Drivers in Formulas](/syntax/drivers-syntax/using-drivers-in-formulas.md)