calculation of probability of default on debt interest and its repayment

Aanjan16y ago

To calculate probability of default on debt I have learnt two methods..
i) z(Number of standard deviation)= distance to default/standard deviation
ii) calculated as N(d*) where, d*= In(Pa/Pe) +(u-0.5s^2)t / s*square root T
I m confused which method should be used for calculating probability of default particularly when debt is repayable after 5 year how to use first method in that situation..i would b thankful if you could help me getting through this confusion with illustration

Bbasilisk16y ago#1

Black - Scholes model assumes that underlying stock is distributed lognormally. I'll try to illustrate:

S0 - current price, S - price in one year (lognormally distributed random variable). Assume that Rs is annual return on S. Then S/S0=exp(Rs), assuming continious compounding. Or ln(S/S0) = Rs - random variable. Volatility of Rs (which is actually normally distributed) is used in Black - Scholes formula.
Prediction of default
Assume that V - value of assets of the comany today, F - debt payable (in t years), if V distributed lognormally, using black-scholes formula you can calculate 'value firms equity as european call option' (from BPP study text):

E=N(d1)V-N(d2)F*exp(-rt)
d1=(ln(V/F)+(r+0,5*sigma^2)t/(sigma*sqrt(t))
d2=d1-sigma*sqrt(t), where sigma is volatility of ln(V) (in BPP study text sigma is volatility of V, which is inconsistent with Black-Scholes model assumptions)

1-N(d2) is the probability of default (when option is out of the money).

In Q3 from December 2008, for example, examiner in answers assumes that cashflow is distributed normally, then he calculates expected annual cashflow and its volatility, and finally probability that cash outflow is greater than cash in hand.

I did some simulations in Excel, and found that in 500 tries I had no default, I suspect there is a problem in examiner's solution with calculation of annual deviation.

P.S. having read solutions to the exam questions, I would recommend just to do something (assume normality, for example), if you get stuck :) .

Aanjan16y ago#2

thanks for reply...but still i m confused..let me ask you to solve a question for me..
Anjan Plc asset's market value is $55million..it wishes to raise $10 million to finance new project..repayable at the end of year 3 from now..its asset volatility is 40% p.a..
Bank's base rate is 5.25%...level of recovery on default is 70%..
what interest rate per annum bank would charge to compensate its perceived level of risk.?

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