Total potential rewards: STU  
STU  author  50 STU  curators 

25 SBD 
256.66 Steem Power


25 STEEM 

24.67 USD
25 USD 

Total USD: 62.17 USD 
Starting with HF 20/21, the distribution algorithm changed, favoring more rewards to curators. This explanation is updated for that change.
The main confusion point is the "$" displayed by default near the rewards by Steemit (and busy, and eSteem). This "$" is not a USD. It has nothing to do with it. It's also not a SBD. So, what is it? It's what I'l call from now on a "Steem Token Unit", or STU. This is different from SBD and STEEM as currencies, and it's actually the expression of the underlying value storage in the STEEM blockchain, which goes under the name vests.
So, the potential reward you see near your posts is actually expressed in STU.
Example: you see near your post $100. In order to understand how much you will get, we will talk form now on in STU whenever we refer to the numbers the Steemit UI is showing. So you actually see near your post 100 STU.
Out of this, you give away 50% from your STU to curators.
You remain with 50 STU.
This amount is split 50 / 50, with the following algorithm:
Please note the difference: you get SBD directly as half of your rewards, but you get your Steem Power at the current market price of STEEM, not in absolute numbers.
You get half as SBD, and half as USD equivalent value expressed in SP, at the current price of SP in USD.
The end result for something that displays 100 STU near your post:
Let's see how much this means in fiat at the following prices: STEEM = $6, SBD = $8.
So $100 displayed rewards, are actually equal = $424.96 real USD.
Let's see how much this means in fiat at the following prices: STEEM = $6, SBD = $8.
So $100 displayed rewards, are actually equal = $449.92 real USD.
Feel free to play with the sliders above and test various scenarios.