Place the tracking code on redirecting pages.
If your site uses redirects, the redirecting page becomes the landing page's referrer. For example, if you've changed your site so that index.html now redirects to home.html, then index.html becomes the referrer for home.html. If someone reached your site via a Google search that sent them first to index.html, you won't have any data regarding the Google search.
For this reason, you should place the Google Analytics tracking code on the redirecting page as well as on the landing page. This way, the redirecting page will capture the actual referrer information for your reports.
Refer to Introduction to analytics.js to learn more about Google Analytics tracking code.
Refer to the Google Analytics (Universal Analytics) tag if you use Google Tag Manager to manage your Google Analytics tracking.