You are not able to do calculations in Pipedrive Direct.
You can potentially use a zap to calculate the commission [if its a simple formula based on the deal amount]
Hi @Matt Oehlert our teams have calculated fields and commission in the back of their heads but no immediate plans right now. We're first working on mandatory fields 🚀
Thanks for the suggestion though, will pass it along. For now probably it's best to use Zapier to calculate commission. I've also seen people simply export monthly to Excel and run calculations there.