Wondering if anybody knows if any websites exist for converting options prices into the price of the underlying and the vice versa as well. For example, if I buy a spy option for a dollar, I would use this site to determine what spy would be at when the option is worth 0.90. I know its pretty simple math when the contract is at expiry, but im wondering what the underlying and option would be at during the time I use the site to calculate this. Any help is appreciated.