Recently on a Google Tag Manager/Google Analytics Facebook forum, some asked if a site already has Google Analytics (GA) implemented then will there be any issue if they also put Google Tag Manager (GTM) on the site.
Specifically this person wanted to use GTM for other tags e.g. Facebook pixel and leave Google Analytics on the page and not implement via GTM, He was mainly concerned that by implementing Google Tag Manger, his Google Analytics reporting will be messed up and start double counting everything.
The simple answer to this question is: GTM and GA are two different products and have no relationship unless you implement Google Analytics tags via Google Tag Manager. So if you put both codes, GA and GTM on the page, there won’t be any issue.
You can use GTM and use it for other tags, it won’t interfere with Google Analytics reporting.
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