Frixxxx
Moderator
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[TD="class: alignLeft"]Your Personal Investment Performance (PIP) for the past 12 months ending 08/31/2014 is 14.5%.
(Your PIP is posted by the 3rd business day of each month.)
Last month it was only 5.35%. I dropped August 2013 (-2.76%) and added August 2014 (+4.41%) for a difference of +7.17%. So, you would think that my PIP would be closer to +12.52%. I'm obviously not computing all that goes into it, but I'll take it.
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From Tsp.gov:
https://www.tsp.gov/sitehelp/glossary/glossaryOfTerms.shtml
Personal Investment Performance (PIP) — The rate of return earned by your entire account during the 12-month period ending on the date indicated on your annual statement or on your Account Balance page of the TSP website. The PIP is a time-weighted return that has been calculated using a modified-Deitz method (a method used by many financial institutions and an industry standard). The PIP adjusts for the distorting effects of cash flows into or out of your account. It is an estimate; therefore, your PIP may not be the same as the 12-month performance of the TSP funds, which are time-weighted returns.
The Dietz method is a good read, but in depth. You can't just add/subtract performance.