When reading your AdWords reports in Google Analytics, there are many possible reasons why there may be discrepancies between Google Analytics visits and AdWords clicks.  If you see wildly different numbers for visits and clicks, the likely culprit is that the AdWords auto-tagging parameter is being stripped from the landing page URL.

What happens when you have auto-tagging enabled in your AdWords account?  Any time one of your ads is clicked on, AdWords will automatically append a paramater called the gclid (Google CLick ID) on to the end of the ad’s destination URL.

For example, if your ad’s destination URL is http://www.mysite.com/landing_page.html and a user clicks on your ad, AdWords will redirect the user to http://www.mysite.com/landing_page.html?gclid=123fa35fjn809080jk (the gclid value is a random string)

The gclid value is a unique identifier that identifies which ad (and consequently keyword, ad group and campaign) the visitor clicked on to reach your site.  When Google Analytics processes your reports, it fills in the AdWords reports by looking up the appropriate gclid values in the AdWords database to find the corresponding information.

Here’s the key point: Google Analytics cannot tell if the visitor came from an AdWords click if the gclid parameter is missing on the page that the user eventually lands on!

The key is to test whether your landing page retains the gclid parameter.

1. Take your destination URL (eg http://www.yoursite.com/landing_page.html) and paste it into your browser’s location bar (where you usually type in a web address)
2. Add a test parameter on to the end of the URL.  If your URL does not already have parameters in it, append ?gclid=test.  If there are already parameters, append &gclid=test on to the end.  (For example, http://www.yoursite.com/landing_page.html becomes http://www.yoursite.com/landing_page.html?gclid=test; and http://www.yoursite.com/landing_page.html?myval=1 becomes http://www.yoursite.com/landing_page.html?myval=1&gclid=test)
3. Press enter
4. Your browser will take you to your landing page.  Be mindful of redirects, especially if you are tracking with Doubleclick, Atlas, etc tags.
5. Is the gclid=test parameter still visible in your browser’s location bar?

YES? Auto-tagging plays nice with your destination URLs.  You can stop reading now!

NO? Oh-oh.  There is most likely an intermediate redirect that is stripping out the gclid parameter. There are two options to remedy this:

1. First (and easiest) – change your destination URL to the ultimate page that the visitor lands on, thus bypassing any redirects
2. Configure your server so that the gclid parameter is passed along in the redirect

(Two other common culprits are users are landing on a 404 error page or the Google Analytics tracking code missing altogether on the landing page!)

There you have it – how to test if your destination URLs play nice with auto-tagging.  For more information, read Google’s help center article on auto-tagging.