How do I measure ROI from my marketing campaigns?

Measuring marketing ROI requires tracking both costs and revenue from campaigns. Set up proper conversion tracking to attribute revenue to campaigns. Calculate ROI as (Revenue - Cost) / Cost × 100. Track costs accurately including ad spend, tool costs, and time. Use attribution models appropriate for your sales cycle. Consider customer lifetime value, not just first purchase. Account for assisted conversions where campaigns help but don't directly convert. Example: A campaign with $10,000 spend generating $40,000 revenue shows 300% ROI, but considering customer lifetime value of $200 instead of $100 first purchase, ROI increases to 600%.