How do you calculate how much you need to save for a home down payment?

I am currently trying to save up for a down payment on a new house. I know I want to save for a 20% down payment (so I don't have to pay for PMI insurance). I've looked at homes in the $800K to $900K range (I know it's expensive but that's what homes are like in my area). I've heard that closing costs are usually 1-3% of the home price. I realize I probably don't have the full amount I would need to buy a house, but I am curious on the formula to calculate how much you would need to save up. **What is the percentage of the home price that typically makes up what you need for a down payment and closing costs combined?**