15% of your net income for child support however if she was to claim income support she would only recieve £10 p/w of this, i think it goes up to £15 or £20 p/w end of this month.Child tax credits would pay more for being a lone parent.Housing benefit if she is in rented accommodation
When she is back at work working min of 16 hours she would be entitled to working tax credits.
However depending on your earnings and ability to pay you may have to pay her x amount to not make her a burden on the state.
In the wikivorce library there is a section about benefits
http://www.wikivorce.com/divorce/Benefits/Check-your-benefit-entitlement.htmlhave a look on the link above.