A long runway would be long enough to meet a huge milestone with your current funding. Given a standard milestone (reaching profitability, reach profitability

A long runway would be long enough to meet a huge milestone with your current funding. Given a standard milestone (reaching profitability, reach profitability in some markets, user growth to XYZ threshold), 1.5 years is probably solid and 2.5-3 years is "long". Practically speaking, there is little difference between 3 years and 10 years of runway, because a company that stagnates for 3 years is likely to lose key employees and momentum whether or not there is money left in the bank. The goal of a startup isn't necessarily to survive at all costs, it is to make sure to survive long enough to see if the concept works. That is where there is no exact answer, because it depends. If you are a startup where increasing revenue isn't on the near-term road map, you might want to be more conservative because you will eventually be depending on investors in the future. If you are a startup with really strong unit economics and a path to profitability, you can be more aggressive because in the worst case scenario you can probably reach profitability via the backdoor (layoffs, cutting expenses, etc).