# Frequency Rules

This article explains **frequency rules** for variables in Model Reef.

You will learn:

* How variable frequency is defined.
* How frequency interacts with model periodicity.
* How to choose sensible frequencies for different types of variables.

Frequency describes how often a variable **accrues** within the model timeline.

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### Variable frequency vs model periodicity

The **model periodicity** sets the base grid, for example:

* Weekly
* Monthly
* Quarterly
* Yearly

Each variable has a **frequency or schedule** that tells the timing engine how often accruals occur.

In most cases:

* Variable frequency is aligned with model periodicity (for example a monthly variable in a monthly model).
* You can also represent one-off events, quarterly items in a monthly model, or annual items in a quarterly model using schedules.
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### Common frequency settings

Typical patterns:

* **Every period**
  * Revenue or Opex variables that recur each week or month.
* **Quarterly**
  * Tax instalments, some professional fees, certain leases.
* **Annual**
  * Registration fees, annual insurance, one-off retainers.
* **One off**
  * Single payments, unusual items, one-time events.

You express these through the variable's timing settings using either simple frequency choices or explicit schedules.
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### Frequency and amount patterns

Frequency interacts with amount patterns as follows:

* A variable can have the **same amount each time it accrues** (for example a fixed retainer).
* Or it can use drivers or formulas to vary amounts period by period even if the frequency is regular.
* Range-based presets can spread a total amount evenly across a range of periods.

The timing engine uses frequency to decide **when** to apply the calculated amounts.
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### Frequency and model changes

If you change the model's periodicity:

* The model timeline is regenerated.
* Variable frequencies are interpreted against the new base grid.
* Accrual patterns are updated accordingly.

For example, if you move from a monthly to a quarterly model:

* Monthly repeating variables aggregate naturally into quarters.
* Quarterly variables may become single events inside each quarter.
* One-off events are mapped to the quarter that contains their date.

You should always review key variables after changing periodicity to ensure behaviour still aligns with your intent.
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### Choosing frequencies in practice

Guidelines:

* Use **every period** for most recurring revenue, COGS and Opex items.
* Use **quarterly or annual** for items that genuinely occur that way, such as some tax or regulatory fees.
* Use **one off** for major non-recurring events such as large one-time projects.
* Avoid using unnecessarily complex frequencies when a simpler pattern plus drivers will do.

Clean frequency choices keep the timing model understandable and traceable for reviewers.
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## Related articles

* [Production Budgeting & Delivery Models](/use-cases/media-agencies-and-creative-studios/production-budgeting-and-delivery-models.md)
* [Build a Cost of Goods Model](/how-tos/operations-and-unit-economics/build-a-cost-of-goods-model.md)
* [Terminal Value Rules](/help/financial-outputs-and-valuation/terminal-value-rules.md)
* [Start & End Dates](/syntax/timing-syntax/start-and-end-dates.md)


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