Do you have to be great at mental math to do HF?

I'd say as long as you are not doing quant, mental math is not a necessite. In my experience, this skill is helpful for us to quicly spot some mistakes our analysts make in their calculations. Most times, it was the fundamental analysis that matters the most, which cannot be achieved without a detail research. Making logical and thorough inference is what I consider as the most crucial skill.

Thanks much appreciated

Previously I had a PM who couldn't stress mental math more. He would constantly drill me on forecasting revenue based off growth percentages, applying multiples to those figures, etc. Another PM I worked for couldn't have cared less. In my experience it is shop to shop. 

I mean I feel If I worked at it I could become good. I wish I had taken more time earlier in life to do that. Difficult now given the job. But unsure if part of it is just how you were wired.

Personally I think mental math translates to agility of mind and ability to think quickly. Which matters in this job.

Maybe small sample bias, but I don’t trust judgment of people that are below average with mental math when this job is about processing overabundance of data points and signal and digesting them in an efficient manner.

If you can I'd at least make an effort to enjoy doing simple math in your head. flawless mental math makes people immediately think you are sharp which is one of the only things seniors care about.

Because the truth is most of your job performance at the junior levels is just following instructions and remembering to double check numbers. You aren't getting paid to do math at all but you definitely don't want to be a guy who makes math mistakes 

Being quick can be helpful, but I don't think its necessary unless you're in a role in which not being quick is a liability (ex: a trader that has to decide on a trade in 10 seconds). ADHD is going to be a problem if you make mistakes though.

As long as you do not rush your work or answers, if you know you have a weakness do not put a spotlight on it. Many people in this industry have near photographic memories, amazing mental math and can quickly spot when data/pattern makes no sense. Others need to dig deep and go full Michael Burry to really have confidence in their view. Just always play to your strengths. 

Forget about Quant hedge fund not becuase your mental math but becuase of your math skills. Quant position require intensive math skills equivalent to mathematical or computational finance degree. Some statistics skills will lead you to risk management position. proficiant Python coding skills can make you coder at many financial institutions. 

No you don’t need to be good at mental math. I’m quite bad at it, but I think divergent thinking is more important on the job 

I think you have to be comfortable with numbers and be able to interpret them and simplify them to think on the fly. With that said, excel was invented for a reason and the key skill worth spending time on is having good logic and critical thinking skills because that’s how you source and identify patterns and ideas and develop an edge.