This is one of those "too easy" setups.
Dollar reversed from bullish to bearish trend in January of 2017. Created a lower low on A-Leg. Retracing to the 0.618 of the fall for B-Leg. Now preparing for next big leg down, with a 20% decline.
The scary thing about this, is I do not see that actually being the stopping point for the dollar. That's just the technical location of it's fall. It is likely to do a little bounce there, but, resume the downtrend WAY deeper after that.
Timing is very difficult for this. It could take anywhere from a couple of months to several years to do this 20% decline.
Be mindful that a bull trap could be set, sending DXY up to around 99, the 70.2% retrace, before the fall occurs. Otherwise, the 61.8% retrace is totally acceptable as completing this wave.