You can calculate VTR (View-Through Rate) for your YouTube ads using this simple formula:
VTR = (Completed Views ÷ Impressions) × 100
So if your skippable ad was shown (impressions) 10,000 times and 2,500 viewers watched it to the end (completed views), your VTR would be:
(2,500 ÷ 10,000) × 100 = 25%
This helps you see how many viewers stayed engaged with your ad instead of skipping it.