Coast FIRE means you have enough money in your retirement account to have a secure retirement without contributing any additional funds
Social security, pensions, and 401Ks are all traditional retirement income sources, but you might have a side hustle or other investments as well
How are you going to spend your golden years? Your costs will vary depending on what you are planning to do with your new-found free time
Add up all of your monthly and yearly expenses to see how much your life typically costs per year
What will inflation be like? How much will your medical bills costs? What else don't you know?