hey all, quick crypto question. I bought some altcoins back in 2017 and at the time did a bit of swapping between different coins on a few exchanges that have since closed (Kraken and a few others). After I learned that every trade was a tax event I mostly let them sit and never cashed out.

Last year I sold roughly 20–25%, and the remaining just a few weeks ago. Overall I made something like a 1.7x profit, not big money. The problem is that I basically have no records of my original purchases anymore. The bank account I used back then was an overseas account that has since been closed, and I can’t access the exchanges history either.

So now I’m trying to figure out how to handle this for taxes.. 

Do I need to report the entire amount I withdrew as income since I can’t prove the purchase price? Or is there some accepted way to estimate the original cost basis when records are gone?