Hi @stefang285,

Thanks for reaching out to the Klaviyo Community!

There are a few ways you can do this:

• The easiest way to accomplish this split is through our “Random Sample” functionality. What you’ll do is determine the size of half this list. For example, if it’s a list of 10K contacts, you’ll know that half of that audience is 5K. You will then click into the list > click the “Manage List” dropdown > click “Random Sample”  and then enter in the number that is half the audience. This will create a new list with half the volume of the original list. You will send one campaign to this audience and then when you go to send your second campaign, you’ll send to the original list but make sure to EXCLUE the random sample list from that send. This will give you the other half of the list.
• Another option would be export the original list as a csv > split that csv into 2 csvs with even number of contacts > import each csv as it’s own list.

Hope this helps! 

Julie