As you know when you work with data you have always need a Time dimension table .There are a number of ways of building these tables :

• External data source like Azure Market place
• Power Query
• Excel File

In Excel 2016, you can get one built automatically inside the Power Pivot window.

You can create your date Dimension starting from other Table. For example if you have a Fact table of sales with date column loaded into the Data Model, when you go to the Design tab in the Power Pivot window you’ll see the new Date Table button enabled:

Clicking on the New button will add a new date table to the Data Model, called Calendar:

If you want to change date you have the option of manually configuring the range of dates used by clicking the Update Range button:

If you do make changes like adding calculated columns, such as the Month Year calculated column shown below:

You can then click the Save Configuration button to save the current state of the table as your default.