This paper estimates the cost of mental health problems to UK employers for the financial year 2016/17, updating previous figures published by the Centre for Mental Health. It calculates business costs due to sickness absence, reduced productivity when staff are at work or 'presenteeism', and in relation to replacing staff who leave their jobs for mental health reasons. The estimates show that costs to employers come to £34.9 billion for the financial year 2016/17, equivalent to approximately £1,300 for every employee in the UK workforce. The findings show that improving mental health in the workplace makes good business sense. It highlights the need for organisations to promote wellbeing, create healthy work environments, support those experiencing mental ill-health and equip employees returning to work.