In YNAB, if I have a very large unexpected expense in a bucket that doesn't have that much money in it yet, do I pull from other categories to cover it or will the negative value roll over for the next x months until enough money goes into it to cover it?

You transfer from other categories to cover it.

Or perhaps from Ready to Assign if you can afford it and don’t want to take it from your other categories.

while technically true, I would urge people to always have ready to assign as 0

Right that would be ideal. I.e., once someone has their monthly expenses figured out for the most part.

I tend to not have any money in my ready to assign category, since anything extra goes to taxable investments. I guess - what's better to do - pull from other buckets to leave the investing amount or should I take out of investments to leave my monthly budget static

Not necessarily, you might value those taxable investments more than other buckets you’ve been saving for

Unfortunately the reason I don't usually have Ready to Assign at 0 is because it's a pain to transfer from other categories and much simpler to assign directly from Ready to Assign

So interesting! I definitely don't find it to be a pain at all and I love being able to see in the recent moves column where I made actual priority decisions of one category over the other.

It's not always so much of it being a pain as much as how easy it is to just assign more money. There are also 2 ways of transferring: 1. you overspend on a category and go to the 'Cover overspending'. This way is simpler because you just select which categories to transfer money from. If category B doesn't cover the entire overspending of category A, you can then select category C to help cover the rest. 2. you anticipate additional spending and transfer from another category. This is more of a hassle since you have to select the category and then type in the exact amount you'd like to transfer. Neither of these are a crazy pain, it's just so much easier to have a small amount in Ready to assign bc the UX of assigning is much simpler.

Whatever works and keeps you using it! I think your way is easier, but less intentional about where you pull money from, which is probably better for some people (including yourself)

correct, it's not always necessary to hone in on the exact category where I'm pulling from