How do you determine the Lease Price

Ok I’m new to Lease Options, so please answer kindly… :shocked
My question is this I’m looking to do a Lease Option here in California, but I can’t seem to determine the option price in 18 months.
My sandwich lease will be for 12 months

Please explain how you all determine future price.

I did look for this topic, but did not find what I needed…

Thank you kindly

You can’t. That’s purely speculation.