Cost Basis vs Average Book Value

qosmioamit

What is the difference between Cost Basis and Average Book Value?
For some of my holdings, the two are the same number; and for other holdings, they are not the same.

VidasMatelis

Lets say you had following transactions for the same symbol:
2020-01-01 Buy Qty:10, Price:10, Total Amnt:100
2020-01-10 Sell Qty:10, Price: 11, Total Amnt: 110
2020-02-02 Buy Qty: 100, Price: 12, Total Amnt: 1200

So you bought symbol, then sold all the shares and then bough again that same symbol.
Avg Book value will include all transactions for that symbol that increased book value (DAX Formula):

Avg Book Value:=CALCULATE(
   DIVIDE(SUMX(Trans, Trans[TotalAmnt]*Report[TransReportExchRate])
      , SUMX(Trans, Trans[QtyChange])
  )
   , FILTER(TransType, OR(TransType[BookValueSign]=1, TransType[TransType]="Split"))
   , DatesBetween(Dates[Date], Blank(), LastDate(Dates[Date]))
) * Report[Qty Held]

Calculation with numbers:
(100+1200) / (10+100) ) * 100 = 1300/110 * 100 = 11.82 * 100 = 1182

Cost basis is much more expensive (resource wise) operation and will create "chain" of buy/sell transactions and will understand that before last buy you had 0 quantity of that symbol, so all cost basis comes just from the last transaction, that is 1200$.

If you are just accumulating shares and do not sell them yet, then Avg Cost Basis is a quick way to see how much you paid for your shares.