DateTime objects may be compared using PowerShell's comparison operators:

$date1 = (Get-Date).AddDays(-20) 
$date2 = (Get-Date).AddDays(1) 
$date2 -gt $date1 

Dates can be compared to a string; the value on the right-hand side will be converted to a DateTime. As with casting with parameters, a great deal of care is required for date formats other than US.

For example, in the UK I might write the following, yet the comparison will fail. The value on the left will convert to 13^th January, 2017, but the value on the right will convert to 1^st December, 2017:

(Get-Date "13/01/2017") -gt "12/01/2017" 

The corrected comparison is:

(Get-Date "13/01/2017") -gt "01/12/2017"