Alternative and more realistic calculation:

Situation 2025: You have 1 BTC and want to have, each 4 years, the same amount in USD. The rest will be sold or spent as "passive income".

Price evolution:

Let's say that we hit a 140,000 ATH this year and have then new ATHs each 4 years with 70% of the previous cycle profit.

- 2025: 140,000 (100% profit compared to previous ATH of 69,000$)
- 2029 240.000 $ (70% previous ATH - 0.7 * 100%)
- 2033 360.000 $ (49% previous ATH - 0.7 * 70%)
- 2037 480.000 $ (34% previous ATH - 0.7 * 49%)
- 2041 600.000 $ (24% previous ATH - 0.7 * 34%)

We simplify greatly here: let's say 2025-28, 2029-32 etc. the price is exactly the same and then it jumps to the next level.

You then need the following amount of BTC to hold your USD value. The difference between your current holdings and the holdings at the "last level" is the payout you can afford without losing USD value:

- 2025-28: 1 BTC - no payout
- 2029-32: 0.58 BTC - payout; 0.42 BTC in 4 years, 0.105 BTC per year, ~0.009 BTC per month (2200$)
- 2033-36: 0.38 BTC - payout: 0.2 BTC in 4 years, 0.05 BTC per year, ~0.005 BTC per month (1700$)
- 2037-40: 0.29 BTC - payout: 0.09 BTC in 4 years, 0.0225 BTC per year, ~0.002 BTC per month (960$)
- 2041-44: 0.23 BTC - payout: 0.06 BTC in 4 years, 0.015 per year, ~0.0011 BTC per month (660$)

So you get the idea, right? With a shrinking volatility there is no stable passive income, instead the value you can afford to pay out gets lower and lower. Nevertheless the idea may not be that bad.