If you start your project on the day a LTS comes out, you'll theoretically be compatible with the _next_ LTS, 2 years later, so in some ways it's up to 5 years

If you start your project on the day a LTS comes out, you'll theoretically be compatible with the _next_ LTS, 2 years later, so in some ways it's up to 5 years until you need to change your code.