During 2020, I did 100 crypto trades: buying/selling many type of crypto currencies. I used an online service (Bitcoin.tax) to calculate my tax liability for 2020 tax year. It processed all my trades and generated final numbers for Turbotax software.
Then during 2021, I did 50 trades (buying/selling). Some of them on new crypto and some on whatever crypto I had left from the year earlier.
Situation: I am working on 2021 taxes now. I want to use a different service (Cointracker.io or something else) to calculate my 2021 tax liability.
Question 1: Does 2021 service needs my 2020 details to calculate accurate numbers? What information does 2021 service needs from 2020 service?
Question 2: What are the best practices of doing taxes of crypto trades?