In implementations of systems for simultaneously modifying multiple variable fonts, a computing device implements a modification system to identify a first range of values of a glyph attribute that are adjustable by changing values of a particular design axis of a first variable font that is common to the first variable font and a second variable font. The modification system identifies a second range of values of the glyph attribute that are adjustable by changing values of the particular design axis of the second variable font. An overlapping range of values of the glyph attribute is determined between the first range of values and the second range of values. The modification system generates an additional instance of the first variable font and an additional instance of the second variable font for display in a user interface based on the overlapping range of values of the glyph attribute.