Diagnostic and statistical manual of mental disorders, fifth edition (DSM-5) 
SAD is not considered to be a unique diagnostic entity, but rather a specifier to describe subpopulations of patients with recurrent major depressive disorders, bipolar I disorder, and bipolar II disorder, with variations in the onset, intensity, and remission of symptoms following a temporal pattern. Patients meeting DSM-5 diagnostic criteria for recurrent major depressive disorder and bipolar I and II disorders are assessed according to additional criteria. A seasonal subspecifier is applied if the following criteria are met:
A regular temporal relationship exists between the onset of mood symptoms and a particular time of year that is not better accounted for by seasonally related psychosocial stressors (e.g., seasonal unemployment, bereavement, trauma).
Full remission of mood symptoms (or change from depression to hypomanic/manic symptoms) occurs at a regular time of year (e.g., resolution of depressive symptoms during the spring).
Over the last 2 years, at least 2 major depressive episodes have occurred that demonstrate the temporal seasonal pattern, without evidence of nonseasonal major depressive episodes occurring during that same time period.
Over the lifetime course, the number of seasonal major depressive episodes substantially outnumbers nonseasonal major depressive episodes.
The current severity of SAD may also be further documented according to the number of criterion symptoms present, the severity of those symptoms, and the degree of functional impairment associated with the condition:
Mild: enough symptoms present to meet diagnostic criteria, distressing but manageable symptoms, with minor impairment in functioning.
Moderate: increased number of symptoms beyond those required for the diagnosis, more intense symptomatic presentation causing increased impairments in social or occupational functioning.
Severe: number of symptoms substantially in excess of those required for the diagnosis, symptoms are seriously distressing and resulting in substantial functional impairment.
SAD may be further specified as being either in partial remission (i.e., symptoms from last seasonal episode are still present, yet full diagnostic criteria are not met, or full remission of symptoms for a sustained period lasting less than 2 months) or full remission (i.e., no significant symptoms present for at least 2 months).
Symptom changes may not be as severe in subsyndromal presentations of SAD. Patients may not meet DSM-5 criteria for a clinical mood disorder. However, the mood disruption and impairments may be sufficient to initiate treatment.