You can calculate ROI by number of blocks per day 576(2.5min average block time) x 67.5 mn reword ÷ number of mn. Yesterday I recieved 11 rewords nearly 750. The wallet is showing around 83 mn but not all are active. So currently I would say 576 x 67.5= 38,800 ÷ active mn. Around 9-12 rewords per day currently 500-800mun would be my best estimate.