Anyone know of a source for an Excel spreadsheet (free) that calcualtes IV given all other inputs? TIA

Not sure if this meets your request but there is a spreadsheet named "implied_volatility.xls" in a long list of free financial spreadsheets: http://www.gummy-stuff.org/Excel/

That would be sorta what I'm looking for. However, they get an IV of 14.5 for their example whereas my BS formula in a spreadsheet and a stand alone program indicate that it's more like 22 (scratching head).

Here is a C++ implementation of the Method of Bisections, by Bernt Odegaard. #include <cmath> #include "fin_recipes.h" double option price implied volatility call black scholes bisections(constdouble& S, constdouble& K, constdouble& r, constdouble& time, constdouble& option price){ if (option price<0.99*(S K*exp( time*r))){ //checkforarbitrageviolations. return 0.0; //Optionpriceistoolowifthishappens }; //simplebinomialsearchfortheimpliedvolatility. //reliesonthevalueoftheoptionincreasinginvolatility constdouble ACCURACY =1.0e 5; //makethissmallerforhigheraccuracy constint MAX ITERATIONS =100; constdouble HIGH VALUE =1e10; constdouble ERROR = 1e40; //wanttobracketsigma.rstndamaximumsigmabyndingasigma //withaestimatedpricehigherthantheactualprice. double sigma low=1e 5; double sigma high=0.3; double price = option price call black scholes(S,K,r,sigma high,time); while (price < option price){ sigma high =2.0* sigma high; //keepdoubling. price = option price call black scholes(S,K,r,sigma high,time); if (sigma high>HIGH VALUE) return ERROR; //panic,somethingwrong. }; for (int i=0;i<MAX ITERATIONS;i++){ double sigma =(sigma low+sigma high)*0.5; price = option price call black scholes(S,K,r,sigma,time); double test =(price option price); if (fabs(test)<ACCURACY){ return sigma;}; if (test < 0.0){ sigma low = sigma;} else { sigma high = sigma;} }; return ERROR; };

http://www.google.com/search?q=blac...s=org.mozilla:en-US:official&client=firefox-a http://www.google.com/search?q=impl...s=org.mozilla:en-US:official&client=firefox-a

Excel VBA IV Function. Function ImpliedCallVolatility(UnderlyingPrice, ExercisePrice, Time, Interest, Target, Dividend) High = 5 Low = 0 Do While (High - Low) > 0.0001 If CallOption(UnderlyingPrice, ExercisePrice, Time, Interest, (High + Low) / 2, Dividend) > Target Then High = (High + Low) / 2 Else: Low = (High + Low) / 2 End If Loop ImpliedCallVolatility = (High + Low) / 2 End Function '=========================================== Function ImpliedPutVolatility(UnderlyingPrice, ExercisePrice, Time, Interest, Target, Dividend) High = 5 Low = 0 Do While (High - Low) > 0.0001 If PutOption(UnderlyingPrice, ExercisePrice, Time, Interest, (High + Low) / 2, Dividend) > Target Then High = (High + Low) / 2 Else: Low = (High + Low) / 2 End If Loop ImpliedPutVolatility = (High + Low) / 2 End Function

Thanks for the suggestions. I've looked at a lot of links but haven't found exactly what I'm after yet. It's out there somewhere.

Have you seen this here, spindr0? There's a bit of VBA code (it's on the second page and written by none other than Collector) that implements the Newton-Raphson method. http://www.wilmott.com/messageview.cfm?catid=4&threadid=3656

Many functions to look through here http://www.smartxl.com/ "The Collector" has lots of functions on his site, but takes time to find them on the site. http://www.espenhaug.com/ Carl