How do you decide when a side project is worth turning into a startup?

From the investor side: flattery scales infinitely and costs nothing. Retention and willingness to pay don't.

What I actually look at

Two numbers tell most of the story:

1. How many people return in week four.
2. How many would be genuinely upset if the product vanished tomorrow.

Everything else is noise until those two are healthy.

Going full-time isn't a reward for a good idea. It's a bet that you can survive eighteen months of it being hard.

So before you jump, ask whether the worst version of the next year is one you can actually live through.