This article describes modifications, that can be done with dates in Power Query (Get and Transform).

It is about changes done in “New column”, but changes in “Transform” are very similar. 

Age

Provides the days, hours, minutes, seconds and parts of seconds from date to today. So, it is changed after any recalculation.

Date only

Removes the information about time.

Parse

Changes the text containing date to normal date. Makes sense for text only – otherwise this option is not available.

Year

There are multiple options here. Year provides the number of year (2017), Start of Year first day of year (1.1.2017) and End of Year, surprisingly, last day of year (31.12.2017).

Month

Similar to previous, with additional option Name of Month (March, for example…)

Quarter

Similar to previous.

Week

Provides the number of week in year, and, of course, end and start of week.

Day

Just read the menu…

Substract Days

Substracts two dates. Available only when to columns are selected.

Combine Date and Time

Merges column with date and column with time. Available only when to columns (date and time) are selected.

Earliest, Latest

Finds the earliest or latest day. The result is just one value – so it makes no sense for New Column, it only works for Transform.