Much research and policy attention has been on socio-economic gaps in participation at university, but less attention has been paid to socio-economic gaps in graduates' earnings. This paper addresses this shortfall using tax and student loan administrative data to investigate the variation in earnings of English graduates by socio-economic background. We find that graduates from higher income families (with median income of around 77,000) have average earnings which are 20% higher than those from lower income families (with median income of around £26,000). Once we condition on institution and subject choices, this premium roughly halves, to around 10%. The premium grows with age and is larger for men, in particular for men at the most selective universities. We estimate the extent to which different institutions and subjects appear to deliver good earnings for relatively less well off students, highlighting the strong performance of medicine, economics, law, business, engineering, technology and computer science, as well as the prominent London-based universities.