That is a hard question to answer and the problem faced is that it is a different amount for everyone. I feel that I need close to what I earn now per year. My husband feels he needs less as we will live more simply, not need to travel for work and will relax more. What makes it more difficult, is that we don’t know what things will cost in 30 years.
I feel that most people underestimate their requirements. We live longer, the pensions are getting less and one day will be gone. Most of us make a poor job of planning for the future. I don’t want to return to work at 75 because I will have already spent my retirement funds.
People of my mother’s or grandmother’s generation had a pension and there was nothing to think about. While this has already been mentioned; it does mean that we perhaps should not be taking advise from someone who did no planning for their retirement and how to invest to get there.