Can you verify your calculations?
Of course.
Look at
block 4500 on the block explorer. (The last Proof Of Work block)
Outstanding coins = 913,277.500272311Deduct the Outstanding Coins value above from that of the current block. Using
block 21588 at the time I type this:
Outstanding coins = 913,595.438148831913,595.438148831 - 913,277.500272311 = 317.93787652
Block 4500 was created at 4:19 am (GMT) on 18th July that's currently ~2 hours short of 16 days.
317.93787652 / 16 = 19.8711172825
20% interests per annum is not equivalent to 316 coins in 16 or 17 days (I assumed daily compounding of interests).
You're also assuming everyone is staking.
Bittrex holds ~47% of all coins and most of their wallet addresses seem to be flagged as belonging to them. I don't think I've ever seen one of those flagged addresses staking.