Advertisement Continue Reading Below First input delay is more than trying to please Google. Improvements to site performance generally lead to increased sales, ad revenue and leads. Definition of First Input Delay FID is the measurement of the time it takes for a browser to respond to a site visitor’s first interaction with the site while the site is loading. This is sometimes called Input Latency. An interaction can be tapping a button, a link or a key press and the response given in response. Text input areas, dropdowns, and checkboxes are other kinds of interaction points that FID will measure.