# Entering Seasonality

This article explains how to **enter seasonality** in Model Reef input fields.

You will learn:

* What seasonality represents in the model.
* How to input seasonal patterns as multipliers or absolute values.
* How seasonality interacts with base values, schedules and delays.

Seasonality is used to reflect consistent patterns over each year, such as busy and quiet periods.

## 1. What seasonality means

Seasonality typically captures:

* Higher sales in certain months or quarters.
* Lower activity in off-peak periods.
* Repeating patterns year after year.

Rather than modelling each period independently, you define a pattern that repeats across years unless changed.

## 2. Ways to enter seasonality

You can usually enter seasonality as:

* **Multipliers** — percentages or factors that adjust a base value up or down by month.
* **Patterned time series** — explicit monthly values that repeat on a yearly cycle.

Examples of multipliers:

* January: `0.8`
* February: `0.9`
* March: `1.1`
* Peak months: `1.3`

The engine applies these to the underlying base series for the variable or driver.

## 3. Combining seasonality with base drivers

A common pattern is:

* Set a **base annual or monthly value** using a driver or formula.
* Apply seasonal multipliers to spread that base across months.

For example:

* Annual forecast revenue for a product.
* Seasonal multipliers allocate more of that revenue into peak months.

This keeps total volume consistent while shaping the intra-year profile.

## 4. Seasonality and schedules

Seasonality can work alongside schedules:

* A schedule defines when events are allowed or expected to occur.
* Seasonality modifies the magnitude of those events by period.

For instance:

* A monthly schedule for revenue recognition.
* A seasonal pattern that increases volumes in months with predictable spikes.

The combination allows detailed timing and pattern modelling without writing custom formulas for every month.

## 5. Editing and updating seasonality

{% stepper %}
{% step %}

### Open the variable or driver

Open the relevant variable or driver in the model editor.
{% endstep %}

{% step %}

### Access the seasonality controls

Access the seasonality section (often via the Timing modal or a dedicated panel).
{% endstep %}

{% step %}

### Adjust multipliers or explicit values

Update multipliers or explicit monthly pattern values as needed.
{% endstep %}

{% step %}

### Review the resulting series

Review the resulting series or preview chart to confirm the changes.
{% endstep %}
{% endstepper %}

You can revise seasonality as you learn more about actual behaviour, without rebuilding the underlying variable logic.

## 6. Validating seasonal assumptions

After setting seasonality:

* Visually inspect the time series to confirm peaks and troughs match expectations.
* Check that annual totals still match high-level targets if you intended them to.
* Compare against historical actuals where available for sanity checks.

Correctly capturing seasonality improves both accuracy and credibility of the model.

## Related articles

* [Entering Accruals & Delays](/syntax/how-input-fields-work/entering-accruals-and-delays.md)
* [Seasonality Inputs](/syntax/timing-syntax/seasonality-inputs.md)
* [Aggregate Categories](/help/building-your-model/aggregate-categories.md)
* [Build a Seasonality Adjusted Forecast](/how-tos/scenarios-and-planning/build-a-seasonality-adjusted-forecast.md)


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