Productivity gain = 5%
This is a very modest assumption. Many studies suggest that the differences between productivity of those with low well-being and high can be as much as 30%. 

Days lost through absenteeism a year = 4 – 8 days
New figures released in the height of the recession in the UK suggest that absenteeism is at an all time low of just 4.5 days. Fear and insecurity can also reduce absenteeism but these gains will probably be lost as and when the economy recovers. People wanting to be at work is a better motivator for reducing absenteeism and has the added benefit people also being present and energised.

Staff turnover = 16% at a cost of 40% of annual wage.
The average figure for the UK is 16%, for the US it seems to be higher but the US has stronger seasonal effects than the UK. We take the UK figure here. The costs of each member of staff leaving are assumed to be 40% of annual wage. It will be significantly lower for seasonal work (hence low US turnover assumption) but higher for senior management positions. This estimate includes the direct costs of recruiting as well as knock-on effects of hiring temporary staff and/or increased burdens on existing staff. (source Sainsbury Centre for Mental Health – as above)

Gallup, 2013

Gallup, 2013