To get to $20k by end of the year using just steady growth, not even with a new boom phase starting, would just take an average of $320 gains per week.
There's 36 weeks left in the year, BTC is at $8500. That's $11,500 to go to break the ATH and touch $20k. Comes out to $320 per week. I don't think anyone would say a $320 weekly gain for Bitcoin is very much. Granted it has to average that over 36 weeks, but still, looking at it this way $20k in 2018, building up to a 2019 boom, seems like it won't be that hard.
Should be a good year for making money from these prices onward!
That is assuming if bitcoin continues its dominant growth shown through the last week.
I personally don't think that we're going to see an all time high being broken this year. We very rarely see markets make a full recovery and go on an ultra-bull run that fast, within 1 year. As I've said, I feel like although currently the rally may take us to $9.5k+, it's most likely not going to crack $10k yet. Even if it does, the downward selling pressure may start mounting soon after we're above 5 figures.
Also, bitcoin growth is never this regular. We never see every single week of the year being in the green.
I'm leaning towards 2020 as the next main bull market, it should be quite easy for BTC to crack the all time high set last year then. But this year, I don't think it's happening.