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Time Value of Money - important formula

Tan KW
Publish date: Sun, 07 Apr 2013, 04:11 PM
Tan KW
0 460,865
Good.

FV - Future Value 

PV - Present Value

R - Compouand annual return

n - Investment horizon

EAR - Effective Annual Rate

Pn - Price at the end of n

Pn-1 - Price at the end of n-1

 

Simple Valuation

FV = PV * (1+R)^n

PV = FV/ (1+R)^n

R = (FV/PV)^(1/n) - 1

n = ln(FV/PV)/ln(1+R)

 

If n is infinite

 
PV   = FV / ( 1 + R ) +  FV / ( 1 + R )2  +  FV / ( 1 + R )3  +  .  .  . 
 
dividing each site with (1+R) ,
PV/(1+R) = FV / ( 1 + R )2  +  FV / ( 1 + R )3 +  FV / ( 1 + R )4  +  .  .  .
 
PV - PV/(1+R) =  FV / ( 1 + R )
PV(1+R)  - PV = FV
PV + PV * R - PV = FV
PV * R = FV
 
PV = FV/R

 

 

If n is infinite and Growing FV

 
PV   =  FV/ ( 1 + R ) +  FV(1+g) / ( 1 + R )2  +  FV(1+g)2 / ( 1 + R )3  +  .  .  . 
 
multiply each side by (1+g)/(1 + R)
PV(1+g)/(1+R)   =  FV(1+g)/ ( 1 + R ) 2  +  FV(1+g)2 / ( 1 + R )3  +  .  .  . 
 
PV - PV(1+g)/(1+R)= FV / ( 1 + R )
 
PV(1+R) - PV(1+g) = FV
PV + PV * R - PV - PV*g = FV
PV * R - PV * g = FV
PV(R - g) = FV
 
PV = FV/(R-g)

 

Compounding

Compounding occurs m times per year  --> FV = PV(1+R/m)^(n*m)

Conitnuos Compounding - m is infinite --> FV = PV*e^(R*n), e = 2.71828

 

Effective Annual Rate (EAR)

Compounding occurs m times per year  --> PV(1+R/m)^(n*m) = PV(1+ EAR)^n  --> EAR = (1+R/m)^(m) - 1

Conitnuos Compounding - m is infinitve --> PV*e^(R*n)= PV(1+ EAR)^n --> EAR = e^(R)- 1

 

Stock Return Calculations

Net return over n period --> Rn = (Pn - Pn-1)/Pn-1

Gross return over n period --> 1 + Rn = (Pn)/Pn-1

Multiple period returns

Net Return, Rn(2) = (Pn - Pn-2)/Pn-2 = (Pn/Pn-2) - 1

Relationship to 1 period returns

Net Return, Rn(2) = (Pn/Pn-2) - 1 = (Pn/Pn-1) * (Pn-1/Pn-2) - 1 = (1+Rn) * (1+Rn-1) - 1

Gross Return,1+Rn(2) = (1+Rn) * (1+Rn-1)

!!! 2 period gross return = the product of 2 1-period gross returns

K-period return

Net Return, Rn(k) = (Pn / Pn-k) - 1

Gross Return,1+Rn(k)  = (1+Rn) * (1+Rn-1) * (1+Rn-2) ....... * (1+Rn-k+1)

 

Portfolio Return Calculations

SA = % of Stock B, RA = return of Stock A

SB = % of Stock B, RB = return of Stock B

SA + SB = 100%

 

FV for Stock A = (PV*SA)*(1+ RA)

 

FV for Stock B =  (PV*SB)*(1+ RB)

 

 
FV for Portfolio, FVp =  (PV*SA)*(1+ RA) + (PV*SB)*(1+ RB) 

 

                                     = PV * [SA*(1+ RA) + SB*(1+ RB)]

 

 

                                     = PV * [SA + SA*RA + SB + SB*RB]

 


                                     = PV * [1 + SA*RA  + SB*RB]
 
Return of Portfolio, Rp
PV(1 + Rp) = PV * [1 + SA*RA  + SB*RB]

 

Rp = SA*RA + SB * RB

!!! For a portfolio with Z stocks, Rp = SA*RA + SB * RB + ...... + SZ*RZ
 
 
Stock Return Calculations (with dividend)

Dn = dividend received

Net Return, R = (Pn + Dn - Pn-1)/ Pn-1

Gross Return, 1 + R =  (Pn + Dn)/ Pn-1

 

Stock Return Calculations (with inflation)

Ifn = Inflation over period n

Deflated price by using Inflation, Pr = P/Ifn

Return with Infaltion, Ri = (Pr - Prn-1) / Prn-1

                                            = ( (P/Ifn) - (Pn-1/Ifn-1))/ (Pn-1/Ifn-1)

                                            = (Pn/Pn-1) * (Ifn-1/Ifn) - 1

                       

Annualizing Returns

 

Rm = Monthly Return

 

Ra = Annual Return
 
If same montly return for 12 months, Ra = (1+Rm)^12 - 1
 
 
Continuosly Compounded Returns

continuosly compounded return, r = ln(1+R) = ln(Pn/Pn-1)

given r, R = e^r - 1

r is alway smaller than R

 

 

says r = R/m, where m is infinite

e^r = e^(ln(1+R))

       = e^(ln(Pn/Pn-1))

       = Pn/Pn-1

Pn = Pn-1 * e^r

 

!!! see "Notes on natural log and exponential functions" sections for more details on natural log functions

 

 

Multiple period returns 

r(2) =ln(Pn/Pn-2)

       = ln(Pn/Pn-1 x Pn-1/Pn-2)

       = ln(Pn/Pn-1) + ln(Pn-1/Pn-2)

       = r period n + r period n -1

!!! cc returns are additive

 

Portfolio returns 

 

Rp = SA*RA + SB * RB

rp = ln(1+Rp) = ln(1 + (SA*RA + SB * RB))    <> SA*rA + SB * rB  --> portoflio cc returns are not additive

 

Return with Inflation

 

Ri  = (Pn/Pn-1) * (Ifn-1/Ifn) - 1

1 + Ri = (Pn/Pn-1) * (Ifn-1/Ifn)

ri = ln(1 + Ri)

   = ln( (Pn/Pn-1) * (Ifn-1/Ifn) )

   = ln( (Pn/Pn-1)) +  ln(  (Ifn-1/Ifn) )

   = ln(Pn) - ln(Pn-1) + ln(Ifn-1) - ln(Ifn)

   = r + ln(Ifn-1) - ln(Ifn)

 

Notes on natural log and exponential functions

e = 2.7183

ln(e^x) = x, e^ln(x) = x

ln(x * y) = ln(x) + ln(y)

ln(x/y) = ln(x) - ln(y)

ln(x^y) = y * ln(x)

e^x * e^y = e^(x+y)

(e^x)^y = e^(x * y)

 

 

 

Discussions
4 people like this. Showing 3 of 3 comments

sharemania

thanks for the sharing. useful indeed !

2013-04-08 08:43

KowChye

very complicated. Life should be much simple. So is earning money.

2013-04-10 12:51

Hustle

Investment is a bit complicated,punting just up/down only hehe

2013-04-10 12:52

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