The core formula is ROI = ((Revenue attributed − Total campaign cost) ÷ Total campaign cost) × 100, expressed as a percentage, while ROAS = Revenue ÷ Cost, expressed as a ratio. The formula is the easy part. The number it produces is only as honest as three inputs most brands get wrong: total cost, which routinely omits gifting, shipping, licensing, and management time and inflates ROI by 15 to 30%; the attribution window, since most influencer purchases happen 7 to 30 days a
