For employee working for private companies, union, or state and local governments, you have 180 calendar days (less than 6 months) from the last date of the discrimination or retaliation to file a charge of discrimination with the EEOC. Simply contacting the EEOC is not the same as actually filing a charge. However, an attorney can file a charge for you and send it to the EEOC. Where and When I Can File an EEOC Charge.
In most discrimination cases, your 180 days begins to run as soon as you receive clear and unambiguous notice that the employer has subjected you, or is in the future going to subject you, to an adverse employment action. It is best to consult an attorney and file a charge as soon as you know the minimally necessary information, and not wait until you know as much as possible.