The math gets a little tricky here, but here's a neat trick to at least let you know if you should be worried: The value of the put option with the same strike and expiration is a quick and dirty proxy for the time value of the call.
- Why's this true? I understand the following quote.
John Hull. Options, Futures, and Other Derivatives (2017 10 edn). p 216.
The excess of an option’s value over its intrinsic value is the option’s time value. The total value of an option is therefore the sum of its intrinsic value and its time value.
- How accurate and precise is this proxy?