Given initial XTZ of approx 750M, assuming 5% per year, this is 37.5M new XTZ the first year.
Now, in the alphanet, each block can have 15 endorsements, and both generation & endorsement are each worth 150 XTZ reward. But with my calcs, for 5% yearly NDI, it would equate to approx 4.46 XTZ reward for either of these tasks.
Assuming 37.5M new XTZ per year, 1 minute block time, and 16 blocks & endorsements per day, this equates to 8409600 blocks+endorsements per year and if you divide 37.5M be that 8409600, thats where I come up with the 4.46 XTZ reward per block/endorsement.
Now, that may all change - It appears in alphanet that I endorse about 10x more than I generate a block.
So who really knows. Just thought this was some interesting math to lay out.
And check out the progress on my delegation wallet: https://wallet.tezzigator.com/Status