I always seem to cook a lot more than what needs to be.
I am paranoid about falling short on something when I have guests coming over to dine. So, I rather end up cooking excess and the food gets wasted.
How can I improve my estimates?

it's hard to judge exactly how much someone is going to eat - especially when you have guests over! you don't want too little because they may be afraid to take what they want and yet you don't want tons of leftovers - it's not easy!

maybe you can make your own TV dinners and freeze them for a later date so that nothing gets wasted.