There is a huge list of possible causes behind the differences in statistics of Adwords and Analytics. In this text we will explain the cause of this problem step by step. In part A) we will discuss differences in clicks, in part B) differences in conversion percentage.

Part A) Differences in Adwords clicks, and Analytics visitors.

Differences between "clicks" and "visits" are almost always there. This is normal as we are comparing apples and pears. A click measured by Adwords is not the same as a visit measured by Analytics. Causes of these differences:

1) An Analytics visit or "session" lasts 30 minutes

Google Analytics measures a visit as a chain of pageviews. To belong, according to Analytics, to the same visit, these pageviews have to be measured within 30 minutes apart from each other. If a visitor doesn't do any action on your site for longer than 30 minutes the next action will be registered as a new visit. An example: Somebody clicks on your Adwords advertisement in the Google search results. This click is registered by Adwords. Next, this person browses on your site for a while and then leaves your site to compare prices with the site of a competitor. After 15 minutes this person realises you have the best offer and by a second click on the same Adwords advertisement he/she gets back to your website. Right now Adwords has registered two clicks. Because everything took place within the limit of 30 minutes, Analytics will only measure one visit.

2) Adwords filters invalid clicks, Analytics does not.

It regularly happens a visitor clicks an Adwords ad for other reasons than the aim of the ad. For example by a computer program which automatically clicks on advertisements to raise the click percentage, Web crawlers who index your website or maybe a competitor who wants you to get higher costs. To prevent you from getting targeted by such “invalid clicks”, Google Adwords filters these out and the costs are waived. These clicks also get removed from the Adwords system so your statistics do not get contaminated. Analytics, however, can not see the difference between a normal and an invalid click and registers both as a visit. Your Adwords account shows how many invalid clicks are measured within a certain period of time.

3) "Auto-tagging" is not activated

Within Google Analytics you can see which visitors came on your website by organic search results and which by paid search results. Analytics measures where a click is from via URL tagging. This means the URL (the link) of your advertisements on Google contains a parameter Analytics can read. You can choose to give in a parameter yourself, but for most of us it would be better to use the automated system of Adwords. When “Auto-tagging” is activated, it adds the so called Gclid parameter to the URL and it’s read by Analytics. If you did not activate Auto-tagging and also did not add your own parameters to your URL’s, Analytics can not determine where your visitors are from. Visitors who came to your site via Adwords will now be classified as organic or direct. You can easily activate Auto-tagging in Adwords under the tabpage “My Account” -> “Preferences”.

4) "Apply cost sources" is turned off

Finally to show your Adwords data in Analytics you need to activate this option (="Apply cost sources"). As long as Analytics is correctly linked with Adwords this will not cause any problems. When you checked the box, your Adwords campaigns will be shown in Analytics under Traffic sources -> Advertisements. To activate “Apply cost sources” you need to do the following thing:

Go to your Analytics account for the concerning website -> click on the Administrator tab page -> click on the concerning profile -> click on profile settings -> checkmark “Apply cost sources”.

5) Does your website use "URL rewriting"?

"Server side URL rewriting" means that your server will rewrite the URL's of your website. If, for example, AdwordsRobot.com is entered and is automatically rewritten to www.AdwordsRobot.com, this a form of URL rewriting. In some cases this can cause trouble with the Auto-tagging of Adwords. You can test this very easy by entering your website URL and by adding, by hand, a parameter behind the URL. If your website is www.AdwordsRobot.com/index.html for example, you can test if there is a problem with URL rewriting by testing the following URL: www.AdwordsRobot.com/index.html?gclid=test. This URL should show your normal website. If the URL results in a error page or if it rewrites itself, there is a problem. There can be many causes for this, depending on the method used for rewriting, your server settings or the presence and configuration of a content management system.

6) The landing page refers to another page

If your page refers with the use of a 301 or 302 code it is possible the Google Analytics code is not started the right way. More information about the correct linking of pages can be found here.

7) The concerning page does not get measured by Analytics

Each page you want to measure with Analytics must contain the web tracking code. If the concerning page does not show this code, Analytics can not measure any data. More information about how this code needs to be implemented can be found here.

You can check the operation of your web tracking code in your Analytics Account under the tabpage "Administrator" -> "Tracking info". A second way to check if your code is shown on the concerning page is via the "Page source" view in your browser. Here you need to search for the following code (change UA-XXXXX-X with your tracking ID):

<script type="text/javascript">
  var _gaq = _gaq || [];
  _gaq.push(['_setAccount', 'UA-XXXXX-X']);
  _gaq.push(['_trackPageview']);
  (function() {
     var ga = document.createElement('script'); ga.type = 'text/javascript';
     ga.async = true;
     ga.src = ('https:' == document.location.protocol ? 'https://ssl' :
     'http://www') + '.google-analytics.com/ga.js';
     var s = document.getElementsByTagName('script')[0];
     s.parentNode.insertBefore(ga, s);
   })();
</script>

8) Some visitors have installed the Google Analytics opt out plugin.

A few visitors could have chosen not to be a part of the data transfer to Google Analytics. There is a plug in, made by Google, people can install inside their browser to deactivate the Analytics code. This still means the clicks of this person are measured within Adwords. However, from this person you can not see any data in Analytics.

9) Some visitors have deactivated javascript

It is possible that visitors of your website deactivated javascript inside of his/her browser. This mainly arises from the idea that it would be safer and people will have less risk on viruses. A side effect of this is that the Google Analytics web tracing code can not be started and there can not be measured any data of these persons. In principle this has the same consequence as for the people who have installed a Google Analytics opt out plugin.

10) Visitors return to your website via bookmarks.

If a visitor adds your website to his/her bookmarks, the URL displayed in the browser at that specific moment will be saved for later use. Visits getting to your site through bookmarks, normally are measured as "direct" traffic by Google Analytics. If the visitor makes a bookmark of your website after a click on your Adwords ad, it is possible that the "Gclid" parameter added by Adwords Auto-tagging is saved as well. As a consequence, a next visit through the bookmark is seen as paid search traffic by Analytics. Because of this there are more measured visits within Analytics than clicks from Adwords.

11) Server latency

A visitor can visit your website via an Adwords ad, but leave your page before the Google Analytics code is loaded. You can find more about this subject here.

Part B) Differences in conversion percentages

There can be differences between the conversion percentages from Analytics and Adwords. In this case there can be more causes possible as well from which most are inherent to the used measure method. Analytics and Adwords measure conversions simply in different ways.

1) Timing

A big measuring-method difference between Analytics and Adwords is the date and time whereupon conversion is measured. Google Analytics measures conversion at the moment when it is done and the conversion is shown in the statistics at that time. Adwords, on the other hand, will measure the conversion from an Adwords ad to a click. The conversion will, according to Adwords, take place at the moment of the click. An example: On day 1 somebody clicks on your Adwords ad and enters your site. Adwords registers the click and the statistics show the click at day 1. Analytics registers the visit and also shows this at day 1. The visitor looks around a little bit on your website and decides to think about it for a day. The next day (day 2) he/she buys the product of your website. Google Analytics registers this conversion and shows it at day 2. Adwords registers the conversion and sees it comes from the click of day 1. In the statistics this conversion will be shown at day 1.

2) 1 and many per click conversions in Adwords vs Analytics

The way in which Adwords shows conversions in statistics differs from Analytics. You can show conversions as "1 per click" or as "many per click" while Analytics does not have this function. This allows for differences in conversion percentages. An example: a person clicks on your Adwords ad and buys a product immediately. The next day the same person returns to your site by entering your domain name directly and buys a product again. Adwords now registers 2 conversions coming from 1 click. Analytics has now registered 2 conversions but also 2 visits. - Adwords 1-per-click: - 1 conversion per click - Adwords many-per-click: - 2 conversions per click - Analytics: - 2 conversions per 2 visits

3) Cookie expiration data

Adwords and Analytics use cookies to measure conversions at later time points. The Adwords cookie expires 30 days after the ad has been clicked. Analytics sometimes uses cookies who are active for longer than 30 days. Because of this differences in conversion data can arise. A conversion who is made 31 days after the click on an Adwords ad, can in Analytics still be shown as a Google CPC conversion while this has not been measured in Adwords at all.