# Default Assumptions

## Overview

You do not have to specify every [**Assumption**](/assumptions/introduction-to-assumptions.md) of an Assumption [**Variable**](/variables/variable-basics.md). For instance, you might have a Variable called `One-off costs`, as in the screenshot below. There are 20 periods in our [**Model**](/models/home-tab.md), but we only want to enter Assumptions for two of those periods, March and December 2025.

In this case, we can use a Default Assumption to provide a value for the other periods. The screenshot below shows that we have only selected 2 Assumptions in the [**Time Segment**](/variables/time-segments.md) <mark style="color:green;">**(1)**</mark>, but no warning is shown because we have added a Default Assumption that provides a value of `0` for any period without an Assumption.

<figure><img src="/files/xtifZSdCqHn7jjxBArLL" alt="" width="563"><figcaption><p>Variable using Default Assumption</p></figcaption></figure>

## Adding a Default Assumption

To add a Default Assumption, perform the following steps, as illustrated in the screenshots below.

* In the **Variable dialog**, navigate to the **Default assumption step** <mark style="color:green;">**(1)**</mark> (this will only be shown if `Assumption` Variable type is selected in the **Name and Setup step**
* If your Default Assumption does not already exist, ensure that the **Item statuses** table has its only cell selected <mark style="color:green;">**(2)**</mark>
* Click the **New** button <mark style="color:green;">**(3)**</mark>, which will open an [**Assumptions dialog**](/assumptions/assumptions-wizard.md) <mark style="color:green;">**(4)**</mark> in which to create the Default Assumption
* Enter any details and the value of the Assumption, click **Finish**, and the Assumption will be selected

<figure><img src="/files/vZAsep14pEKSHBb5nLLL" alt=""><figcaption><p>Adding a Default Assumption</p></figcaption></figure>


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