when to apply

Answered

I don't think the previous answer you received properly informs you on what to do. It's not that simple.

Apply Early Decision if and only if the school you are applying to is your TOP CHOICE. Keep in mind that within the ED pool are typical ALDC applicants as well. ALDC stand for recruited "A"thletes, "L"egacy or applicant whose parents attend undergraduate school there "D"evelopment or "D"deans list applicants like wealthy donor kids or VIPS like movie or television or singers, and "C"hildren of faculty or staff. All ALDCs have an advantage over anyone else. Applying ED implies you are not applying to other ED colleges at the same time and if admitted, you are committed to attend. The negative thing is that if you applying for financial aid, you will not know what the other aid packages would have been had you applied to your other 10 or 15 schools. Sometimes Financial Aid is not strong during the ED round, because the college knows it has a captive audience.

Apply Early Action if you want to have a VERY DESIRABLE school locked up before you apply to RD school. Some EA school are restrictive like Yale, Harvard, Stanford, so you can not apply ED or EA to other private schools but you can apply to State schools, rolling admissions schools and military academies. Keep in mind that within the EA pool are typical ALDC applicants as well. ALDC stand for recruited "A"thletes, "L"egacy or applicant whose parents attend undergraduate school there "D"evelopment or "D"deans list applicants like wealthy donor kids or VIPS like movie or television or singers, and "C"hildren of faculty or staff. All ALDCs have an advantage over anyone else. Applying EA implies if admitted, you are not obligated to attend. If you accept the EA offer, and you are applying for financial aid, you will not know what the other aid packages would have been had you applied to your other 10 or 15 schools. Sometimes Financial Aid is not strong during the EA round, because the college knows it has a captive audience.

Apply Regular Decision, if you want to have your application consider in a weaker pool of applicants. Typically, ED and EA have the strongest pool of applicants. If you need more time to get your final grade up, improve your test scores, or improve the quality of your extracurricular activities, it is advised to apply RD because those extra 2 months might actually improve the strength of your application. When you apply RD, you have to wait long for a result. Typically ED/EA deadlines are Nov.1 and you hear back in 6 weeks. With RD, deadlines are Jan 1.-Jan 15. typically, and you hear back in 8-12 weeks. The most popular schools and the ones that get the most applications like Ivys and Elites, often take 3 months to review and make a decision on your file. Some RD deadlines are earlier, especially large state schools like the UC system.

So basically apply ED if that university is your 1st choice, apply EA to unis for a higher acceptance rate, and apply RD for other universities lower in your list/those you feel your profile is not good enough for and need more time to spruce your profile up.