Estimated Arrival Time (ETA) for PowerShell

Ever had a script that takes a long time to run?    Would it be nice to see an estimated time for completion?   Well, the code below is for you.  

Percentage complete is an easy calculation for any loop operation.  Deriving time from that requires us to hold ($start) with the time our loop began.  From there we can multiply out and calculate total seconds.   When total seconds remaining is added to the current time .. then … you have ETA.  Example below.

# Data Source
$sites = Get-SPSite -Limit All
# Initialize Tracking
$start = Get-Date
$i = 0
$total = $sites.Count
# Loop
foreach ($site in $sites) {
	# Progress Tracking
	$i++
	$prct = [Math]::Round((($i / $total) * 100.0), 2)
	$elapsed = (Get-Date) - $start
	$totalTime = ($elapsed.TotalSeconds) / ($prct / 100.0)
	$remain = $totalTime - $elapsed.TotalSeconds
	$eta = (Get-Date).AddSeconds($remain)
	
	# Display
	$file = $site.Url.Split('/')[4]
	Write-Progress -Activity "Backup $file ETA $eta" -Status "$prct" -PercentComplete $prct
	
	# Operation
	Backup-SPSite $site.Url -Path "D:\TEMP\$file.site" -WhatIf
}