Should I put the Google Analytics JS in the <head> or at the end of <body>?
2022 Update
The general help page now states to "Copy and paste the global site tag after the opening <head> tag on each page you want to measure". So they now want it before virtually everything else. This may be due to changes to the tracking scripts.
2020 Update
Google currently suggests three different locations, which is frustrating. I haven't found technical justification for any of them directly from Google.
For static sites the general help page tells us to place the code snippet "before the closing
</head>tag".For dynamic sites (with documents generated by the server), the same site says to put it "immediately after the opening
<body>tag".The developer site, however, still has us putting it "near the top of the
<head>tag and before any other script or CSS tags" for all sites.
These are substantially different locations, and what's best for a particular user may depend on whether collection of partial page loads is desired. Some testing may be in order.
You can put it anywhere you want on page, and ll run anywhere on the page whether it’s in the head or the body. But according to Google support (Add the tracking code directly to your site) it is recommended to it in the head tag, paste it immediately before the closing </head> tag.
Following paragraph from a good article explaining why to put code in head tag
The Pageview is recorded only after that code is loaded up. So the sooner you load the code, the sooner that Pageview is recorded. Let’s say you have a big blog page, and it’s a slow loading one, taking even 10 to 20 seconds to load everything up. If your Google Code doesn’t start until the end of the page, it can get held up, just like the old non-asynchronous code used to hold up OTHER lines of code. Except now it’s holding up the tracking code. If a visitor to your site hits the page, and then leaves it before the tracking code fires the Pageview, then you lose that visitor. They now become a new direct visit to whatever page of the site they landed on. This can make all sorts of data on your site incorrect.
Putting it at the end of the <head> section helps ensure the your metrics are tracked even when a user doesn't let the page finish loading.
They used to tell you to put it at the bottom of the page, before they added support for handling partial loading of pages.
Directly from Google:
One of the main advantages of the asynchronous snippet is that you can position it at the top of the HTML document. This increases the likelihood that the tracking beacon will be sent before the user leaves the page. It is customary to place JavaScript code in the
<head>section, and we recommend placing the snippet at the bottom of the section for best performance.
See Google Analytics Help: Add the tracking code directly to your site
You can put it anywhere you want. I always put tracking code at the end of the page and I've never had any problems.