Seasonal pattern is the key difference.

Differentiating SAD from non-seasonal depression in late winter comes down to the DSM-5 seasonal pattern specifier and a few honest questions about timing.

The DSM-5 doesn’t have a separate SAD diagnosis—it’s a specifier for recurrent major depressive disorder or bipolar disorder. To use it, you need a clear history: depressive episodes that start in fall or winter (not late spring/summer) and fully remit in spring or summer. Crucially, you also need to rule out non-seasonal episodes entirely over the person’s lifetime. If they’ve ever had a depressive episode in July, it’s not a pure seasonal pattern.

In late winter, the overlap is massive. Lots of people are depressed in February. The trick is asking when did this start? If it began in October or November and has been consistent, that’s classic SAD. If it started in January or February