Just received this comment on this post. The question:

Came across this post and had a question….how do you calculate your PRR for the time period when the Annualized PRR is a negative number??

When you enter a negative number into the Excel IRR function you get an error because you can’t raise a negative number to a power (i.e. -8.43% ^ (180/365) = #NUM error).

Thanks for your help…great blog!

Okay, this is easy enough to address. The actual formula for calculating a periodic return is…

**[(1 + ROR)**

^{# of days/365}] – 1In this case, it would like this:

**[(1 – .0843)**

^{180/365}] -1**[.9157**

^{.49315}] -1**.9575 -1**

**-.0425 or -4.25%**

The readers problem was that he tried to perform the calculation using -8.43% rather than its decimal equivalent.

Hope this helps.

**Related:**

Reader Question Regarding Personal Rate of Return

How to Annualize a Rate of Return

Reader Question: How Do You Calculate Compound Growth (or Interest)?