i have 10 ml of 12.5mcg per spray.. how much cologne would i have to added to make it 10mcg per spray?
12.5/10 = 1.25 or 125%
You need to increase the amount of liquid in the bottle by 25% of how much is already there.
25% of 10 mL is 2.5 mL.
So, add 2.5 mL, resulting in 12.5 mL of liquid in total.
This sounds like 5th grade math: “12.5 is what percent of 10?”. But then again, I might not be smarter than a 5th grader 
, so don’t take my math as gospel.
I’m more wondering why you would want to make such a small adjustment? Which product is it?
If it is 10ml from a 30ml, simply decanting 5ml into a togo and taking advantage of its smaller spray size would probably take you near enough to the 10mcg for most practical purposes.
i have 3-4 different p’s that are unscented and after using em unscented (didnt notice anything) and then adding ammo scent on top (iois but too strong of a smell) i would rather add a lil bit of the scent in to the bottles and just thought 10mcg would be good dose to keep track
so is 2.5 ml right?