This question already has an answer here:
I don't think there will be a canonical answer for this question. I'm just wondering if this is how it works.
It's said that when you kill someone, you split your soul. I believe that means you split it in half.
So, I came up with this graph:
The splitted part of the soul couldn't be exactly 1/7 every time because he didn't know how many he would make, perhaps he would make more in the future.
He asked Slughorn about making 7, that's why I'm using this number here.
Perhaps it's just a random percentage of the soul... I don't know.
But, as I said, considering that the soul is split in half.
When he splits it again, I don't think a soul already "horcruxed" would be a part of this division, since it is intact inside another object that could be anywhere in the world.
So, this means that the first Horcrux he made would have half his soul. Then, the second would have 1/4 of it, just as himself.
Does that means that Voldemort fought against Harry in the last book with only 0,78% of his soul in his body?
Is my math insane?