An example of calculating ETA for a PowerShell progress bar.

Example-Progress-ETA.ps1

# Data Source
$items = 1..85

# Loop
$items | ForEach-Object `
    -Begin {
        # Initialize Tracking
        $total = $items.Count
        $start = Get-Date            
        $i = 0
    } `
    -Process {
        # Progress Tracking
	$i++
        $prct = $i / $total

	$elapsed = (Get-Date) - $start
	$totalTime = ($elapsed.TotalSeconds) / $prct
	$remain = $totalTime - $elapsed.TotalSeconds
	$eta = (Get-Date).AddSeconds($remain)

	# Display
	$activity = "Testing ETA"
        $status = ("$($prct.ToString('P')) % ($i/$total) {0:dd\.hh\:mm\:ss} eta $eta" -f (New-TimeSpan -seconds $remain))
        Write-Progress -Activity $activity -Status $status -PercentComplete ($prct * 100)

	# Operation
        Start-Sleep -Milliseconds (Get-Random -Minimum 100 -Maximum 500)
    }