I would say 21 BTC but we are talking about retirement which means life becomes a little boring especially if you aren't spending $$$ hoping for the little in your stash to grow while you seat back..for this the number just went up...maybe 100 Bitcoins would do wonders especially if I can have 20 BTC to spend and continue living while waiting for the rest of the coins to do the heavy lifting maybe grow x5 or x10 etc.
It depends on our lifestyle and where we live and how much is the most reasonable average annual need that we spend. An estimate of $70,000 per year is safe. We just need to divide it by the current BTC price and let's say it's only 100K and our retirement has started now, so, the estimate is around 0.7 BTC × 30 = 21 BTC with a duration of 30 years and this maybe estimation in category safe and comfortable if my assumption.
In my Country Bangladesh, every day with 5 members cost..
Per daily with cost average 20 dollars ...
30 days cost 30×20 = 600 dollars
Annual cost 600×12 =7200 dollars
If Allah gives me 40 years Lifetime then .
40×7200= 288000 dollar ~2.88 BTC