How long does it take to start charging

Hello,

Maybe this is the $1.000.000 question. But lets be serious about it.

Lets assume that you have a good Idea for a product to build. To build the final product can take a long time. In the mean time, one should be also busy talking to potential customers as to keep validating your Idea. But still it could take months to have a usable product. All those months you are building and building and building. No money coming in. I am not talking about salaries but about covering costs.

My Question is when do you start charging customers? On one hand you can't start charging a customer for nothing. On the other hand not charging can be very difficult since you are putting all your time and effort in your product while not earning anything.

I am wondering what your views are on this.

Thanks so much.