Change in the best-fitting masses and ages of transiting exoplanet host stars due to a change in the assumed helium abundance or mixing length parameter. Dots show the best-fitting mass and age for the default values of Y and α_MLT and lines show the change in mass and age due to an increase in helium abundance ΔY = +0.02 (left panel) or a change in mixing length parameter Δα_MLT = −0.2 (right panel). Horizontal lines indicate the age of the Galactic disc (dashed), the age of the Universe (dotted) and the highest age in our grid of stellar models (solid). The curved dotted line shows the terminal age main sequence (TAMS) for stars with solar composition.