# In FX markets, option can be expressed as either call or put. Explain

For example, if option contract has condition: $$AUDUSD = 0.8$$ at the maturity date, and current exchange rate is $$1 AUD = 0.75 USD$$.

For this option, it could be considered a call option on $$USD$$, and put option on $$AUD$$ since $$AUDUSD$$ means that $$AUD$$ is sold 1 to buy $$USD$$ 0.8.

For the call option perspective, I get that strike price is $$0.8$$.

What I don't understand is the strike and spot price of the put option.

Why is it that spot for the put is 1, not 1.33( = 1/0.75), and strike is 0.9375(0.75/0.8), not 1.25( = 1/0.8) ?

Maybe I'm missing some basic concept about Fx or put options?

• “spot for the put is 1”. Where do you get this from?
– dm63
Nov 27, 2021 at 16:56
• You might want to clarify the question as your terminology is non-standard and confusing. Options have expiry dates, not maturity dates, and what you refer to as a "condition" is - I think - the strike price. I assume you're referring to an OTM call on AUD which is a put on USD. You don't start quoting USDAUD just to describe a put on AUD. Nov 27, 2021 at 17:31
• This answer offers a complete Put on JPY = Call on USD calculation. Strike does not change. Nov 27, 2021 at 17:59

• buy $$1$$ USD for $$1/0.8$$ AUD, or equivalently,
• buy $$0.8$$ USD for $$1$$ AUD.
• sell $$1$$ AUD for $$0.8$$ USD (put on AUD with strike $$0.8$$).
To summarize: the call option on $$0.8$$ USD with strike $$1/0.8$$ is the same as a put option on $$1$$ AUD with strike $$0.8$$