1st halving ATH - 10000% gain - 371 days later 2nd halving ATH - 2800% gain - 518 days later
3rd halving ATH ~ 6725% gain = 10000% + 2800% / 2 448 days later = 371 + 518 / 2
Also another note, it looks like Bitcoin slowly creeps up on the previous ATH right before the halving. So i'd expect something like a $14,000-$16,000 Bitcoin rolling into the 2020 halving event.
As always please do your own research, I am not a financial advisor.