Bitcoin: How to Forecast the End of a Trend.

The advance from Dec 2018 seems to be tracing an impulse pattern. Wave 1 is an impulse, wave 2 is a zigzag which neatly predicts flat wave 4 by guideline of alternation.
The fifth wave appears to be tracing an impulse as well; an extension. It's probable that two minute degrees have reached completion at this stage and the market appears to be tracing out the third wave.

So how do you forecast the target for wave 5?
One way is to use an Elliott wave channel. Connect the end of wave 2 and 4. Draw a parallel line along the top of wave 3 to project wave 5 target. It is quite common for wave 5 to end upon reaching the upper boundary line of the channel
In some cases, when wave 3 is uncommonly strong, almost vertical. Draw a parallel line using the top of wave 1 instead of wave 3.
From experience, it's quite advantageous to draw the two upper boundary lines.