Obviously, you will have to know $ you bought at, Current $ and $ you sold.
It's not too hard to figure out if you buy/sell with Fiat.
But if you buy BCT/ETH and use that to buy another coins, it gets REALLY COMPLICATED.
For example, I use Binance.
It shows # of coins I have and its BTC value only.
It shows total Dollar amount I have for all coins but doesn't show each coins'.
When I want to sell/buy, I also have to put 0.00xx BTC value instead of Dollar amount. (BTC value and price of coin I want to buy both Fluctuates, hard to put the right price)
If I trade coin to another coin few times, there is no way I can run stats.
I can only look at the total $ amount and say 'I put in $1000 total, hm I made $200 bucks lol'
How do you keep the track of performances for each coins???
There are many services that help you to lead a portfolio. I like
www.cryptocompare.com. There you can track your portfolio in dollars, even if you trade to bitcoin or etherium. Test it, service multifunctional.