20years = 5times the Bitcoin block would go into halving.

1st Halving: 6.25BTC per block
2nd Halving: 3.125BTC per block
3rd Havling: 1.567BTC per block
4th Halving: 0.783BTC per block
5th Halving: 0.391BTC per block (seems really sad at this point)

I plan to finish my dealing with bitcoin within this four year period before the next halving happens. Unless Bitcoin would be really valuable by then.