What fractions apply to the phases of the moon?

The phases of the moon can be understood in terms of fractions of the moon's illuminated portion as seen from Earth. The new moon represents 0% illumination, the first quarter at 50%, the full moon at 100%, and the last quarter again at 50%. The waxing crescent and waning crescent phases show increasing and decreasing illumination, respectively, covering fractions between 0% and 50%. Similarly, the waxing gibbous and waning gibbous phases represent illumination between 50% and 100%.