PowerShell Date Comparison: Compare Dates the Right Way

To compare dates in PowerShell, make sure both sides are [datetime] values, then use -lt, -gt and -eq. Subtracting one date from another tells you how far apart they are:

$dueDate  = [datetime]'2026-10-15'
$shipDate = [datetime]'2026-10-02'

if ($shipDate -lt $dueDate) { "Shipped $(($dueDate - $shipDate).Days) days before the due date" }
"Equal: $($shipDate -eq $dueDate)"

Output:

Shipped 13 days before the due date
Equal: False

Earlier means smaller, so -lt reads as “before” and -gt as “after.” I ran every example in PowerShell 7.6 and Windows PowerShell 5.1, with the same results.

Why do my date comparisons give the wrong answer?

Dates stored as text compare letter by letter, not by calendar. ‘1’ comes before ‘9’, so October 1 looks earlier than September 30:

"As text:  '10/1/2026' -lt '9/30/2026' = $('10/1/2026' -lt '9/30/2026')"
"As dates: October 1 before September 30? $([datetime]'10/1/2026' -lt [datetime]'9/30/2026')"

Output:

As text:  '10/1/2026' -lt '9/30/2026' = True
As dates: October 1 before September 30? False

Convert strings with [datetime] or ParseExact before comparing. Converting a string to a date covers formats like dd/MM/yyyy.

The left side decides

When one side is a date and the other is text, PowerShell converts the right side to match the left. Put the date on the left:

$cutoff = [datetime]'2026-09-01'

"Date on the left:   [datetime]'2026-01-15' -gt '2026-09-01' = $([datetime]'2026-01-15' -gt '2026-09-01')"
"String on the left: '2026-01-15' -gt `$cutoff            = $('2026-01-15' -gt $cutoff)"

Output:

Date on the left:   [datetime]'2026-01-15' -gt '2026-09-01' = False
String on the left: '2026-01-15' -gt $cutoff            = True

With the string on the left, PowerShell compared two pieces of text and got it wrong.

Compare dates without the time

Two times on the same day aren’t equal. The .Date property sets the time to midnight, so you compare days only:

$loggedIn  = [datetime]'2026-09-28 08:15'
$loggedOut = [datetime]'2026-09-28 17:40'

"Same moment? $($loggedIn -eq $loggedOut)"
"Same day?    $($loggedIn.Date -eq $loggedOut.Date)"
"Same month?  $($loggedIn.ToString('yyyy-MM') -eq ([datetime]'2026-09-02').ToString('yyyy-MM'))"

Output:

Same moment? False
Same day?    True
Same month?  True

To compare just the month or the year, format both dates the same way first, as in the last line.

Find the number of days between two dates

Subtracting dates gives a TimeSpan. Be careful which property you read:

$start = [datetime]'2026-08-29 20:00'
$end   = [datetime]'2026-09-28 08:00'
$span  = $end - $start

"Days:       $($span.Days)"
"TotalDays:  $($span.TotalDays)"
"TotalHours: $($span.TotalHours)"

Output:

Days:       29
TotalDays:  29.5
TotalHours: 708

.Days drops the partial day, while .TotalDays keeps it. Round TotalDays yourself if you need a different rule. The TimeSpan documentation lists all of its properties.

Check if a file is older than 30 days

Compare each file’s LastWriteTime with a cutoff date 30 days ago:

$today  = [datetime]'2026-09-28'
$cutoff = $today.AddDays(-30)

Get-ChildItem -Path C:\psfaqs\Reports -File |
    Where-Object LastWriteTime -LT $cutoff |
    ForEach-Object {
        $age = ($today - $_.LastWriteTime.Date).Days
        '{0,-18} {1:MMM d, yyyy}  ({2} days old)' -f $_.Name, $_.LastWriteTime, $age
    }

Output:

budget-2026.xlsx   Aug 20, 2026  (39 days old)
q1-sales.csv       Mar 31, 2026  (181 days old)
q2-sales.csv       Jun 30, 2026  (90 days old)

I used a fixed today so the output doesn’t change. In a real script, use (Get-Date).AddDays(-30).

Find files changed after a date

With Where-Object’s short syntax, the property is on the left, so a plain date string on the right works:

Get-ChildItem -Path C:\psfaqs\Reports -File |
    Where-Object LastWriteTime -GT '2026-09-01' |
    Select-Object -ExpandProperty Name

Output:

notes.txt
q3-sales.csv

Files changed between two dates

Use -ge for the start and -lt with the day after the end date, so the whole last day counts:

$from = [datetime]'2026-04-01'
$to   = [datetime]'2026-08-31'

Get-ChildItem -Path C:\psfaqs\Reports -File |
    Where-Object { $_.LastWriteTime -ge $from -and $_.LastWriteTime -lt $to.AddDays(1) } |
    Select-Object -ExpandProperty Name

Output:

budget-2026.xlsx
q2-sales.csv

To delete old files instead of listing them, see Remove-Item, and try it with -WhatIf first.

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