Day or months between two dates

[Skip2MiLu]

I have list of product batches that have a Batch Creation and Batch Expiry Date as a Date column types.

I have created two virtual columns respectively:

1. [Batch Expiry] - [Batch Creation]
2. [Batch Expiry] - [Batch Creation] / 30,4167

I thought I could use the following expressions based on what I saw in other posts:

1. [Batch Expiry] vs [Batch Creation]
2. [Batch Expiry] vs [Batch Creation] / 30.4167

I tried using both Number and Decimal column type for the virtual columns but I recieved the following error respectively

The expression is valid but its result type ‘Duration’ is not one of the expected types: Decimal

I get the same for Number column type.

What am I missing here?