I am being very stupid probably but I don't understand the following.
Portfolio 1st Jan valued: -$100
A month later
Portfolio 1st Feb valued: -$45
I calculate the return of the portfolio as,
((-45 / -100) - 1) * 100 = -55%
But as I see the value of your portfolio has increased since -45 > - 100 so why is the return negative?