Forecasting the ROI of multichannel marketing requires estimating the volume of subscribers by channel, conversion rates by channel, assessing the dollar value of a conversion, forecasting volume sent per year by channel, estimating costs by channel, calculating total revenue, total costs, and total conversions, and finally calculating the ROI. To estimate these values, researchers can leverage relevant data and statistics from reputable sources such as Twilio's reports and industry benchmarks. By following seven steps, marketers can create accurate forecasts and compelling business case justifications to support strategic decision-making, ultimately boosting their return on investment with multichannel marketing efforts.