Convert a string to datetime in PowerShell

You can simply cast strings to DateTime:

[DateTime]"2020-7-16"

or

[DateTime]"Jul-16"

or

$myDate = [DateTime]"Jul-16";

And you can format the resulting DateTime variable by doing something like this:

'{0:yyyy-MM-dd}' -f [DateTime]'Jul-16'

or

([DateTime]"Jul-16").ToString('yyyy-MM-dd')

or

$myDate = [DateTime]"Jul-16";
'{0:yyyy-MM-dd}' -f $myDate

You need to specify the format it already has, in order to parse it:

$InvoiceDate = [datetime]::ParseExact($invoice, "dd-MMM-yy", $null)

Now you can output it in the format you need:

$InvoiceDate.ToString('yyyy-MM-dd')

or

'{0:yyyy-MM-dd}' -f $InvoiceDate

Chris Dents' answer has already covered the OPs' question but seeing as this was the top search on google for PowerShell format string as date I thought I'd give a different string example.

If like me, you get the time string like this 20190720170000.000000+000

An important thing to note is you need to use ToUniversalTime() when using [System.Management.ManagementDateTimeConverter] otherwise you get offset times against your input.

PS Code

cls
Write-Host "This example is for the 24hr clock with HH"
Write-Host "ToUniversalTime() must be used when using [System.Management.ManagementDateTimeConverter]"
$my_date_24hr_time   = "20190720170000.000000+000"
$date_format         = "yyyy-MM-dd HH:mm"
[System.Management.ManagementDateTimeConverter]::ToDateTime($my_date_24hr_time).ToUniversalTime();
[System.Management.ManagementDateTimeConverter]::ToDateTime($my_date_24hr_time).ToUniversalTime().ToSTring($date_format)
[datetime]::ParseExact($my_date_24hr_time,"yyyyMMddHHmmss.000000+000",$null).ToSTring($date_format)
Write-Host
Write-Host "-----------------------------"
Write-Host
Write-Host "This example is for the am pm clock with hh"
Write-Host "Again, ToUniversalTime() must be used when using [System.Management.ManagementDateTimeConverter]"
Write-Host
$my_date_ampm_time   = "20190720110000.000000+000"
[System.Management.ManagementDateTimeConverter]::ToDateTime($my_date_ampm_time).ToUniversalTime();
[System.Management.ManagementDateTimeConverter]::ToDateTime($my_date_ampm_time).ToUniversalTime().ToSTring($date_format)
[datetime]::ParseExact($my_date_ampm_time,"yyyyMMddhhmmss.000000+000",$null).ToSTring($date_format)

Output

This example is for the 24hr clock with HH
ToUniversalTime() must be used when using [System.Management.ManagementDateTimeConverter]

20 July 2019 17:00:00
2019-07-20 17:00
2019-07-20 17:00

-----------------------------

This example is for the am pm clock with hh
Again, ToUniversalTime() must be used when using [System.Management.ManagementDateTimeConverter]

20 July 2019 11:00:00
2019-07-20 11:00
2019-07-20 11:00

MS doc on [Management.ManagementDateTimeConverter]:

https://learn.microsoft.com/en-us/dotnet/api/system.management.managementdatetimeconverter?view=dotnet-plat-ext-3.1

$invoice = "Jul-16"
[datetime]$newInvoice = "01-" + $invoice

$newInvoice.ToString("yyyy-MM-dd")

There you go, use a type accelerator, but also into a new var, if you want to use it elsewhere, use it like so: $newInvoice.ToString("yyyy-MM-dd")as $newInvoice will always be in the datetime format, unless you cast it as a string afterwards, but will lose the ability to perform datetime functions - adding days etc...

Hope below helps!

PS C:\Users\aameer>$invoice = $object.'Invoice Month'
$invoice = "01-" + $invoice
[datetime]$Format_date =$invoice

Now type is converted. You can use method or can access any property.

Example :$Format_date.AddDays(5)

It's very easy; in my case it works with;

Input:

$Date = '29-07-2022'

DateFormat Convertion:

[datetime]::parseexact($date, 'dd-MM-yyyy', $null).ToString('dd-MMMM-yyyy')

Output:

I had a different but related need to convert a number (seconds) into days/hours/seconds etc.

$seconds = 41414141
New-Timespan -seconds $seconds