If that's the title, the OP question is difficult to answer with certainty and the exact amount varies. For example, if we look at the level of spending and the life expectancy of a person.

If I had a BTC,  I would first withdraw a certain amount of bitcoin periodically then sell bitcoins in like increments. As for the reasons why I think everyone knows BTC has long term growth potential. For the total pension fund, I think 5 BTC has been very helpful for me to enjoy my little family at dusk,