# Period Selector

This article explains the **Period Selector** in Model Reef.

You will learn:

* Where the Period Selector appears.
* How to change the visible time window.
* How to switch between month, quarter, year and custom period views.

The Period Selector controls how time is displayed in dashboards and reports. It does not change the underlying model data.

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### Where you see the Period Selector

The Period Selector is usually visible in:

* Dashboards and chart views.
* Financial statements such as P\&L, Balance Sheet, Cashflow and Cash Waterfall.
* Some exports where you choose which period range to include.

It is often a date range control plus quick presets.
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### Changing the time window

You can change:

* The **start period**, for example from January 2024 to July 2024.
* The **end period**, for example from December 2025 to June 2026.
* The length of the window, for example 12 months, three years or the full model horizon.

The selector then refreshes charts and tables to show only the chosen window.
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### Aggregation level

In addition to start and end, you can usually set the aggregation level to:

* Monthly.
* Quarterly.
* Half yearly.
* Yearly.
* Financial year based.

Rules:

* Aggregation changes how values are grouped, not how they are calculated.
* If the model is monthly, quarterly and yearly views simply sum the relevant months.
* If the model is weekly or daily, you can still group results into months, quarters or years.

This allows you to move from detailed operational views to board level summaries quickly.
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### Using custom ranges

For specific analyses you can set custom ranges, for example:

* From project start to project completion.
* From the current month to twelve months ahead.
* From a historic base year to the first forecast year.

Custom ranges can be useful for focused presentations or to isolate particular phases of a project or investment.
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### Period Selector and exports

When you export reports or dashboards:

* The export reflects the currently selected period range and aggregation.
* To produce a different time slice you simply adjust the Period Selector and re export.

This makes it easy to generate multiple views for different stakeholders without changing the model itself.
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***

## Related articles

* [Selecting Variables in Sidebar](/syntax/formula-syntax/selecting-variables-in-sidebar.md)
* [Start & End Dates](/syntax/timing-syntax/start-and-end-dates.md)
* [Naming & Structure](/help/getting-started/naming-and-structure-high-level.md)
* [Build a Multi Period Comparison Dashboard](/how-tos/dashboards-and-reporting/build-a-multi-period-comparison-dashboard.md)


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