If you think a little, the calculators can not be exact since they do not know what pool you are in, nor the blocks that the pool has won etc.
So you have to look at it in the long term, you may not win what you say daily but if you find 3 blocks in the month and you get the average, the 3 blocks is an example.
For example I found in a month 4 blocks that for me is like 40 days.
It is necessary to take into account the part of luck that that can not take into account the calculator