A Google forwarding number is a unique phone number Google Ads assigns to route calls to your real business line while recording call details, such as duration, start time, and whether the call connected. It is the mechanism that makes phone calls measurable as conversions.
What it does
When call reporting is on, Google shows a forwarding number in place of your real number, on the ad or on your website, and routes callers through it to your actual line. The caller reaches you normally; Google records the call so it can be counted as a call conversion if it meets your minimum length.
Where it applies
Forwarding numbers back both call sources: the call button on a call asset or call-only ad, and the number on your website once the number-swap snippet is installed. Without a forwarding number in place, the call happens but Google never sees it, so Smart Bidding optimizes as if it did not exist. The consequences are worked through in a call from your ad is not a call from your website.