You can take the ACT up to 12 times, although most students stop at 2-3 retakes. We strongly encourage you to take your final ACT exam at least 6 weeks before your college application deadlines.
Keep in mind that early decision deadlines are typically November 1st and 15th, and standard deadlines generally begin in January. This means that if you are a senior applying for early decision, your last chance to take the ACT is typically the September administration date of your senior year; for standard deadlines, your last chance is typically the December administration date.
Again, keep in mind the ACT often does not always meet the aforementioned score reporting deadlines. When planning your test dates, it’s better to be safe than sorry.