What's wrong with my math? 93,1% was in January 11. Now we have 94,1. It's been 22 days since then. 6*20/30=4
For the 22 day period you chose, progress increased by 1%.
Whereas the 21 day period from 10th - 31st Dec produced a 2% increase.
Double the rate in one day less, which drastically changes your projected delivery date.
This shows that the rate of progress is not consistent across percentage points. As pointed out by
Jonathan0009.
1%(A) does not automatically take the same amount of time as 1%(B).
That's what's wrong with your maths. You've taken a variable and used it as if it were consistent.