How do you value software for investors?

Hi All

Is there a calculation or formula to calculate a specific platform that was developed in-house? An investor are interested to invest in our business but we need to now calculate investment size etc, to do this we are thinking that we should also calculate what our platform is worth as it adds value to our company. The platform was developed in-house and is a crucial part of the business, without it the business cant make any revenue, how do we stick a value to the platform?

Thank you in advance