Don’t assume this is age. It could be a health condition beginning to manifest. Inflammation, vitamin deficiency leading to something bad, etc. Brain fog is a common symptom of many possible issues that may just be taking root. I would see a doctor and make sure I fixed any such issue I could.

Thanks. Would love to have such a solution, but generally, doctor visits are normal.

One giant difference I noticed is my speech. When I was younger I spoke very, very quickly, to the point it was off-putting to some folks. I've always thought people who speak quickly have a fast working brain, so to speak.

Today I speak much more slowly and with more deliberation. Not good or bad, just different. Unfortunately I also find myself searching for a word much more often.

"could be." It could also be _completely normal_ losing one's ability over time by not practicing, and one could get it back by just... doing more practice.

I'm in my mid-20's and I can't do mental math as well as I used to. Why? I don't spend as much time on it now, as I did when I was in school some years ago.

My worry is that is a more permanent health change due to bad habits.

I went back to school with the same fears. It comes back to you.

Genuinely, thanks for sharing. I always want to go back, but fear I'll embarrass myself. Or at least realize my age is catching up eith me.

Out of curiosity, what did you go back for, and how did it go?

Also, I don't think you ought to consider "when I was 17, I could do basic calculus in my head" as a sign of more ability than you have today. The problems were likely not that hard, since you were 17.

Do you practice doing long division every day, without pen and paper? If not, then I think you ought to try that before making the judgement "I can't do it". Practice is very important, especially when it comes to memory intensive tasks. The other key bit is coming up with efficient algorithms for doing division in your head that take into account the pros/cons of memory vs. pen and paper (why should we expect algorithms that run well on paper to be effective in our memory-only execution as well?). Over the years, people have developed a wide variety of "mental arithmetic" algorithms.

Finally, doing long division in your head isn't important. No one will judge you by it, when you're applying for a PhD, and so you should not judge yourself by it. There are way bigger fish to fry, even in mathematics.

Man, you guys are very motivational. Thanks for that.

The point I was attempting to make was that I could store these carry numbers in bulk at one point, but now am lucky to remember a single one.

I only know that as I try to teach my own kid math today. It's frustrating to realize you've 'lost your touch.'

But, you're right, it's really not important day to day.

I would probably have to figure out (or more likely look up) how to do long division these days. I probably haven't done it in decades.

Economics - I took some calculus classes at the local community college to sort of spool up and get back into it. I was the weird old guy asking questions that nobody cared about but it’s been a great experience all around. And honestly the concepts are far more important than than the mental math, we all use calculators now :)

As I assume you know how to do it, carrying numbers in long addition is a short term memory thing. I bet you were roughly as bad at it when you were 17 as you are now. Doing basic calculus in your head is way easier, it's simple multiplication.

isn’t this likely just a matter of practice? at 17 I spent hours a week studying calculus so it was easy… then I stopped using it for 20 years and it’s very difficult.

I feel like I’d get good at calculus or anything by dedicating similar amounts of dedicated study time