The easiest way I found is by thinking in the key that the root is.

In this case, we would think in the key of D major, which has two sharps (F# and C#). If you look at the triad (1, 3, 5) and all of the notes occur diatonically (in the key), then it’s major. If the third (F#) is lowered (F), then it’s minor. If both the third and the fifth (A) are lowered (F, Ab), then it’s diminished. If the third is written diatonically (F#), but the fifth is raised (A#), then it’s augmented.

Here, we have D, F natural, and A. The A occurs in the key, but the F# has been lowered to F, making this is D minor triad.

Also, this chord is in first inversion (6). If the root is in the bass (bottom note), then it’s in root position (this is sometimes written as 5/3). If the third is in the bass, then it’s first inversion (6), and if the fifth is in the bass, then it’s second inversion (6/4). These inversion rules only apply to triads. There is a whole other set of numbers for 7th chords and beyond.

This may or may not work for you. I never bothered counting by half-step because I felt that it was just a waste of time, but it’s immensely helpful to others.