Thank you @steemchiller. How did you work out the formula to estimate payout?
The easy part was clear to me after using Steemit for a while and reading some articles about author rewards. The more difficult part is the curation rewards calculation. I came to my solution by connecting what I already knew, trying out different things and watching the resulting values.
I don't show the gross amount as it is being shown on Steemit. I subtract the calculated curation and beneficiary amounts from the author payout sum, so that we can see how much we really will receive. It's not perfect yet, but it's already coming very near to the real payout amounts.
Not exactly but part of it can be found in 'libraries/chain/util/reward.ccp'. I didn't use anything from the official source for my calculation, because there are major differences between C++ and JS code / dependencies.
I guess it would take more time to convert the C code to JavaScript than just build it from scratch and the best way for me always is 'learning by doing' (without just copying existing code).