Take the number of daily blocks (max 720)
Multiply by the masternode reward (5 vivo)
Divide by number of masternodes (147 as of now)
720*5 = 3600 max coins given to masternodes each day
3600/147 = 24.48 ave coins per masternode per day
This gives a return on investment of ~893% a year
This will go down as more masternodes are added, so the earlier you add your node, the more you will benefit from the high returns.
It's worth noting that, for the blocks (720 in this case), that is the upper figure and can be lower in any 24-hour period. With the recent "difficulty bomb" Vivo and some other currencies were being affected by due to selective mining practices, the block count was significantly less. Also, for coins with low transaction activity (I have 2 masternodes of coins in that situation) similarly the actual number of blocks, and therefore payments, will be less.