Would you mind showing your work? I'd like to see where I went wrong, if I did-
Current net hash rate is around 800T, and there's 3600 BTC a day. 4T is 0.5% of the total hash rate, thus 3600 * 0.005 = 18. So 6T is 27.
There is way more than 3600 BTC a day, because we don't have a confirmation time of 10 minutes.
And that will continue for the foreseeable future, as long as we have an increasing difficulty.
All the mining calculators and calculations like your's don't factor that in, so they are always underestimating.
I think it's silly to use time scales like day, week, month, etc. Bitcoin has it's own time scales - 2016 blocks and 210,000 blocks. By using bitcoin's natural time frames in conjunction with a constant percentage of the network, you get rid of the variability from difficulty increases. For example:
25 BTC/Block
2,016 Blocks/Round
25 * 2,016 = 50,400 BTC/Round
50,400 BTC * 0.5 / 100 = 252 BTC/Round