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.
thats some great statistics, when not a lot of bitcoins will be mined then more people will be using it and more bitcoins will be collected via the transactions, i think the mining will still be ok