Absolute FUV flux density vs. absolute NUV flux density for young (<50 Myr; left) and field-age (∼5 Gyr; right) low-mass stars. Black-lines represent least-squares fits to the data. For the field-age sample, we determine separate fits for higher-mass (>0.35 M⊙) and lower-mass (≤0.35 M⊙) Ms.