增四度（英文：Augmented fourth，简写：A4）是音程的一种。它的转位是同样表示相隔六个半音的减五度，是属于不协和和弦的一种。

要称为增四度，需符合下列条件：

在C调自然音阶中，只有［F-B］一对的半音数目刚好为6，符合增四度的要求。而其他组合，由于半音数目皆为5，只属于纯四度，必须把始音下调一个半音，或将结音升高一个半度，才能符合增四度的要求。结果得出以下的组合：

（注：所有涉及和的皆不在此收录。）

In music theory, the tritone is strictly defined as a musical interval composed of three adjacent whole tones. For instance, the interval from F up to the B above it (in short, F–B) is a tritone as it can be decomposed into the three adjacent whole tones F–G, G–A, and A–B. According to this definition, within a diatonic scale there is only one tritone for each octave. For instance, the above-mentioned interval F–B is the only tritone formed from the notes of the C major scale. A tritone is also commonly defined as an interval spanning six semitones. According to this definition, a diatonic scale contains two tritones for each octave. For instance, the above-mentioned C major scale contains the tritones F–B (from F to the B above it, also called augmented fourth) and B–F (from B to the F above it, also called diminished fifth, semidiapente, or semitritonus).