Percentages are multiplicative, not additive.
If you make a 5% gain, and then have a 5% loss, you are not back to where you started, because 1.05 * 0.95 = 0.9975. The loss that balances out a 5% gain is a (1-1/1.05) ~= 4.76% loss, because 1.05*0.9524 ~= 1.
If inflation was 100%, would you expect your money to lose 100% of its value?
Say you have $1000 cash. Widgets cost $1. You can currently buy 1000 widgets with your cash.
After 5% inflation, widgets now cost $1.05, but you still have the same $1000 cash. You can now only buy $1000/$1.05 = 952.38 widgets. Your money only has 952.38/1000 = 95.238% of the ...
Basically, when a stock price goes down by 50%, my profit is 100% of my sell price. When a stock goes down by 75%, my profit is 300% of my sell price.
I disagree with your premise. When you short a stock, the most that you can make is the proceeds that you receive or 100% of the liability.
If you short a $100 stock, $10k is deposited into your account. If ...
I think you're just doing a variant on percent change.
Percent change calculation is:
(new value/old value) - 1
So to do this with only the percent change, since percent is just "per 100" just do the calculation with base 1. And since you're doing short sales you reverse the new and old values as the sale occurs before the purchase.