The primary star, 55 Cancri A, has a spectral type of K0IV-V, indicating a main sequence or subgiant star. It is smaller in radius and slightly less massive than the Sun, and so is cooler and less luminous. The star has only low emission from its chromosphere, and is not variable in the visible spectrum; but it is variable in X-rays. It is more enriched than the Sun in elements heavier than helium, with 186% the solar abundance of iron; it is therefore classified as a rare "super metal-rich" (SMR) star. This abundance of metal makes estimating the star's age and mass difficult, as evolutionary models are less well defined for such stars. 55 Cancri A also has more carbon than the Sun, with a C/O ratio of 0.78, compared to solar value of 0.55. Age estimates for 55 Cancri A include 7.4–8.7 billion years and 10.2 ± 2.5 billion years.