Click the "Developer" tab, followed by the "Insert" menu. Select the "More Controls" button in the drop-down menu that appears.
Highlight the "Microsoft Date and Time Picker Control" option, then click "OK."
Click on the upper left corner of the cell to which you want to add the calendar and drag your mouse pointer to the cell's bottom-right corner. This will draw a rectangle around the cell.
Release your mouse button to insert the calendar into the cell. Whenever you click on the cell, the calendar drop-down menu will appear.
