It requires some maths (and some faith in the Black-Scholes model, but it works okay in historical simulations), but you can do this instead. To lock in a price

It requires some maths (and some faith in the Black-Scholes model, but it works okay in historical simulations), but you can do this instead. To lock in a price for some stock or foreign currency for a given delivery date: - Buy an European call and write an European put at this value. This neutralizes your exposure to fluctuations in price; OR - Helpfully calculate that the "delta" for delta-hedging this portfolio is 1/[present stock price] and replicate the put/call combo: when the market goes up 1%, you buy 1/S stock; when it goes down 1%, you sell 1/S stock. To see why, look at https://en.wikipedia.org/wiki/Greeks_(finance) https://en.wikipedia.org/wiki/Greeks_(finance) Otherwise: try it with a spreadsheet program.