How long does depression last?

It varies: A major depression can last months to years. With treatment, this is shorter.

Days to years: This question is more complicated than it sounds, as it depends how 'depression' is defined. Major depressive disorder, as described in dsm-iv, lasts at least 2 wks & sometimes up to several years. A very rough guideline is 6 mo if untreated. Other depressions are quick reactions lasting just hours or a few days, while depressive personality (usually mild) can be lifelong. All can be treated.