Acute bronchitis can last up to 90 days.
Acute bronchitis is predominantly caused by viruses. Even after the virus has resolved, the irritation that it may have caused on the lining of the bronchial tubes can still cause symptoms to linger. 
Average Expectations for Bronchitis Symptoms
Though the length of time that bronchitis symptoms linger depend largely on the cause of the condition, the health of the patient, and the body’s ability to fight infections, there is published data on the average time-span involved.
The persistent cough associated with acute bronchitis usually resolves within seven to ten days. Don’t be alarmed if your symptoms persist longer. Up to 50% of patients with acute bronchitis have a cough that lasts up to three weeks. Twenty-five percent have a cough that can last up to a month. In rare cases, the cough can linger for three-six months. Your physician can determine the cause of your bronchitis and develop a treatment plan. 
When to Call the Doctor
It is always wise to seek the advice of a medical professional when you are not feeling well, but even more so when you are experiencing particular symptoms. In the case of bronchitis, you should seek the care of a physician if you experience fever, chills, signs of dehydration, shortness of breath or difficulty breathing, or mucous that is not clear. 
 “Bronchitis – Cedars-Sinai.” Cedars-Sinai – A Non-Profit Hospital in Los Angeles . N.p., n.d. Web. 1 Mar. 2012. <http://www.cedars-sinai.edu/Patients/Health-Conditions/Bronchitis.aspx>.
 HUESTON, M.D, WILLIAM J., and ARCH G. MAINOUS III, PH.D. “Acute Bronchitis.” American Academy of Family Physicians 57.6 (1998): 1270-1276. Print.
 Acute Bronchitis.” Medicinenet.com. N.p., n.d. Web. 1 Mar. 2012. <www.medicinenet.com/bronchitis/page2.htm>