I've been through this with a lot of clients and there is a very simple answer:

Essentially you are always ready. Iterating and validating go hand in hand. You can almost turn this on its head and ask "When should I stop validating and continue iterating?"

Iterating without validation is a risk because you are working in isolation and don't know whether your assumptions are correct. So validation should be built in as part of each and every iteration. That includes pre-MVP, when your startup is still just an idea in your head. In the early days that might mean discussing design drafts over coffee, in the later stages that might mean looking at analytics results and A/B tests.

Think of it as a continuous, ongoing process, a conversation with your target market, rather than a stop/go affair where you disappear into your office for a few weeks and then re-emerge, ready to validate.

Each stage continues until you start to hear the same answers and are not learning anything new. Then it's time to ask new questions and for that you most likely need to move on in your product development cycle.

It would be great to hear more about your product, feel free to get in touch.

Best of luck - Nils

Incidentally, I just wrote a column addressing just this question. You can read it in full here: http://www.inc.com/rahul-varshneya/how-to-validate-a-business-idea-ask-these-5-questions.html

This is a very good question and one that all start ups struggle with. Check this image out, it is the best visual representation of what an MVP should be http://bit.ly/1GasIj1

What is the status of your idea development. Have you built a wheel or a skateboard? The main point being, your idea must be developed enough to give some level of value to the customers and most importantly (a lot of entrepreneurs dont focus on this) a great user experience. It may not be your full vision for the product but it provides a quality service. If you launch an idea that breaks, has loads of bugs, isnt followed up with great service the test of potential is tainted and therefore not a true representation of the need in the market.

If you have a working skateboard launch. If you have a wheel time to rethink how what you can take to market to test and iterate.

If you'd like to discuss further feel free to book a call
Best regards
Steve

In addition to what others have advised, here are my comments:

- Just think if you want to use your product? If not, be a customer of your own product and sell the idea to yourself.
- Make a list of a few influencers whom you know, who are in the same industry. They may not be your target customers but they can certainly understand your product idea. Write them an email for their comments and review; it always helps. I have often done that it works!
- If you have been sharing your insights (not the product idea) at some blogs, events, or communities, recall all the pain points and expectations from the audience and see how these map with your product idea.

I can share more details over a call, if it interests you!

Cheers
- Vinish