How are abortions and miscarriages calculated in determining average life expectancy of a country?

They aren’t counted . Life expectancy is based on live births.

I’m not really sure they would count at all. What @zenvelo said.
I feel that if they did, the average would go way down because abortions and miscarriages happen more than you’d expect and it would really skew the numbers

As far as I know, they aren’t.

They don’t count.

I’m not even sure a full term still birth counts? I doubt it.

Does a live birth with the death happening minutes or just hours later count? I’m not sure.

I’d say it doesn’t count at all as the child is not actually born, so the life expectancy is static at zero