4 months. None of that has been full time as I have a job (wife and baby to provide for). I will start working on this full time as soon as I get funding or enough revenue to pay bills.

Are people using your product?

Yes

How many active users or customers do you have? If you have some particularly valuable customers, who are they? If you're building hardware, how many units have you shipped?

Seeking first customers (~15 current users are friends/family).

Do you have revenue?

No

Idea

Why did you pick this idea to work on? Do you have domain expertise in this area? How do you know people need what you're making?

Why:
The biggest problem I’ve had while learning languages is finding people to practice with. Existing solutions such as italki allow you to find teachers, but lessons are expensive and difficult to schedule due to time differences. Traditional language learning apps are good at gamifying basic vocab/grammar, but only offer very minimal/scripted conversation practice.

Domain expertise:
I have succeeded and failed to learn several languages, both in a classroom setting and on my own. Through my experiences, I’ve become an expert on how to/not to learn languages. The most important thing is to use the language in conversation early and often. Otherwise, you’re less likely to remember what you learn and you’ll lose motivation. E.g., I took 2 years of French in high school and 1 year of Chinese in college, but had no one to talk to; I barely remember anything.

How I know people need it:
In spite of the cost/scheduling inconvenience, 5 million people use italki to schedule lessons with human teachers. Another million use a similar platform, Verbling.

What do you understand about your business that other companies in it just don't get?

Intermediate/advanced learners are the most underserved customers in language learning (traditional apps offer little for them). It should be easy for them to jump in and practice whatever they like/switch languages easily.

Also, it’s best for learners to interact with the same teacher consistently; teachers will be more engaging and tailor feedback to learners as they get to know them, and learners feel more comfortable as they build rapport with the same teacher.

How do or will you make money? How much could you make?

Monthly subscription ($5 for MVP, planning to charge more like $20 after adding more features).

Small plan:
This can be a billion dollar company by getting just 500k subscriptions (500k users*$20/month*12 months=$120,000,000 annual revenue).

Big plan:
6 million people use italki/Verbling to find teachers, paying ~$15-$30/30 minute lesson. I believe I can attract most of them to my app.
6 million users*$20/month*12 months=$1,440,000,000 annual revenue.