The ROI, if anyone had bought Bitcoin before 2011 was 100x approximately from 2012 to 2016. if you bought Bitcoin in 2015 it would be 7X approximately in November of 2021. My math can be wrong and I am open to criticism about it.
in 2011 you were buying for something like 2 dollars so your 100x is 200 dollars. You could have that in Spring of 2013. Later that year the price reached 1000 (500x)
2015 was about 700 dollars. 7x would be close to 5000 so that's your 7x ROI reached in 2017.
Yes your math is off by a lot.
2012 halving - New ATH reached around 1 year after
2016 halving - New ATH reached around 1.5 years after
2020 halving - New ATH reached around 1.5 years after
This doesn't mean anything.
This pattern could repeat but doesn't have to because what changes is the number of bitcoin users who learn from their mistakes. Knowing the halving brings ATH they will surely start investing much sooner this time and that could either lead to the longest bull run ever or to a short one that starts early and finishes early.