Whether or not it's "good enough" depends entirely on the college you're applying to. Less selective colleges and community colleges may be more accepting of lower scores, but highly selective colleges will likely require a much higher score. Your GPA, extracurricular activities, and essays will also play a major role in your application.
To determine your chances, you should:
* Research the colleges you're interested in: Look at their average ACT scores for admitted students. This information is usually available on their websites.
* Consider less selective colleges: Focus on schools that have lower average ACT scores or that are test-optional. Many colleges are moving toward being test-optional, making your GPA and other application materials more important.
* Improve your score if possible: If you're still in high school, consider retaking the ACT. Even a few points can make a difference.
In short, an 18 is not a strong ACT score, but it doesn't automatically disqualify you from college. You'll need to carefully research colleges and strengthen other parts of your application to increase your chances of acceptance.