I will attempt to answer your question here.
You have two different scenarios. The first being the most desirable because you have a set bankroll to bet from, so you can gauge what you win or lose.
In the second scenario, you DO have a certain value. If you lose the money, you will have to pay it. I assume that you are not presenting this to a Board of Directors for investment purposes, so you really need to be able to show yourself how much you won or lost based on your starting bankroll.
If you start the year with $50, and you lose it you have two options. 1) Quit and your yearly percentage loss is 100%. OR2) Add another $50 to your account. If you choose option 2, then you have just increased your initial bankroll to $100. So, if you end the year with $125, you increased your bankroll by 25%.
If you want to seperate this out into years, you need to examine option 1 again. You put $50 in, you lose $50 then you are done.
Year 2, you deposit another $50 in, and you increase this to $125.
Your Year 2 return is 150%, but your overall return is only 25%.
Good Luck either way, but it is very important to be honest with yourself about your winnings/losings.
I have met so many people who will sit down at a BJ table and lose $500, then go get $500 more. When they get up the second time with $600, they will say they won $100.
NO YOU DIDN'T You lost $400.
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Sic 'em
dawgball