As I posted elsewhere in this thread, start by thoroughly understanding and tracking your expenditure patterns including healthcare. Then add some additional buffer for known expenses (kids education, long term care, big ticket maintenance etc). The savings you need to retire is at the minimum (25 * expected yearly expenditure) + buffer.

In my case, I way overshot my savings needs: my current net worth is about 60x my typical yearly expenditure.

I was well paid in my career and saved and invested at least about 70% of my income.