Quantitative Finance Stack Exchange is a question and answer site for finance professionals and academics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am valuing a binary FX option (european) with a defined strike and term (2Y). I'm using a closed form solution based on Black-Scholes framework. How can I derive the appropriate volatility to use from the market data I have?

Market Data (all quoted in implied volatility):

25D Risk Reversal 
25D Butterfly 
10D Risk Reversal
share|improve this question
If you just need a Perl formula: github.com/barrycarter/bcapps/blob/master/bclib.pl#L1214 or in Mathematica: github.com/barrycarter/bcapps/blob/master/nadex.m#L64 – barrycarter Oct 15 '11 at 19:33

Binary options can be replicated (in theory) by trading long and short call options with very close strikes. Take the Black-Scholes formula and differentiate it over the strike. You will need to know the slope of the implied volatility skew around the strike of the binary option. This you can do by fitting a parametric formula (I don't know exactly what is used in FX, also SABR?) to your market data. If your option's strike is not too far away from ATM, you should get a reasonable number.

Disclaimer: I don't specialise in FX.

share|improve this answer

It might be easier to use the Black-Scholes formula for binary options:


then add the distributions for each leg:

Heuristics for calculating theoretical probabilities of being ITM at time T for listed options

and then use numerical methods to calculate what volatility makes the legs match the quotes prices.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.