Seventh Chords

To understand this method of figuring out seventh chords, you must have a basic knowledge of the degrees of the major scale.

I will show you how to find every 7th chord you'll ever need in three patterns and with four rules. Obviously, this will not show you every voicing there is on guitar but it is a start if you really want to try it.
The Three Patterns
Place your fingers where the numbers are.
The numbers represent the degree of that note. (1=root note) Seventh Chord Patterns - Dominant 7

The Four Rules

All of the rules refer to the chord symbol which
is the expression used to name chords

  1. The 5th is natural unless you're told otherwise by the chord symbol
  2. "7" means ♭7
  3. "maj7" means that the 7th is not flatted
  4. "min" (or "m") means to flat the 3rd

7th is flatted
7th and 5th are flatted
7th and 3rd are flatted
7th is natural (not flatted)
Am maj7
3rd is flatted, 7th is natural
Am maj7♭5
3rd and 5th are flatted 7th is natural

Note: When you see "aug" or "+" raise the 5th a half step

What you must do is adjust the patterns according to chord symbol.
Examples are shown below.
Dominant 7 vs Major 7

Dominant 7 vs Minor 7