I suppose an answer to your question is when the amount of carbs you eat gives you a blood sugar which is always in range, but as we all know that’s like looking for a chicken with a golden egg ,
I’ve been “ at it” over 40 years and still couldn’t say for certain , all I do know is that if I don’t experiment I’ll never find out , have had various professionals over the years explain about various things from carb counting to injection techniques blah blah blah , at the end of the day we have to find out what works for us as individuals , when your newly diagnosed it’s so difficult to actual grasp hold of the experimenting as your told to do this this and this ,and are wary of doing something wrong , totally understandable, but I was told years ago by a great guy , don’t let diabetes become a “ prison sentence “ finding out what works for you as an individual is definitely a step away for the prison sentence in my humble opinion