Percent Calc Problem

You didn't label your answer... gott have them units on there.
if a short position is in the reds, say $-200, and then makes some gains so that now the position is worth $-100, then how much is this last PL change, expressed in percentage? Is it +100% or +50%?

PL change = fitty percent.

 

In such cases with both positive numbers I use this formula:
pct_chg = endval / startval * 100 - 100
ie. for the above case:
pct_chg = 100 / 25 * 100 - 100 = 300 (not 400%)

I see. But I think in this simple case of just 1 position from t0 to t1 it's both the same:
"percentage gain in PL" and "percentage gain in the account".
I practically mean the account change in percent of such a single position,
but as said with negative numbers at both t0 and t1, where t1 > t0.

And: I wonder if there exist a math formula that covers all cases (incl. negative values) of such percent calculations.
The page(s) about "percentage" at Wikipedia don't even mention any negative numbers, so they were useless in this case. :-(

 

That's the question, Watson! Are you sure?
My math says different: +100%, as said in prev posting.

 

To turn a result negative just multiply by -1

OP still has given too little info. Their loss (negative) of course.

 

Or use val = -val

I don't think so. Everything is already there.
And FYI: "they are", not "their"

 

Don't think so.

They are loss?

 

From -200 to -100 is a gain, a 100% gain, ie. a doubling.

 

yep.
The water under which this trade exists (the negative value) is half as deep at the second measurement point as it was at the first measurement point.
fitty. lol
Secondly, of what value is knowing this redonkulous measure in the first place.

 

What did you gain?
You reduced the negative value. by fitty.

 

The debt was reduced by 100%, not 50%.