Some IPs will work on annual figures for an annual bonus, some will divide it between normal salary payments whilst others will deal with it as a whole in one month --- confusing I know ! You will need to speak to your IP and ask them how they intend to treat it.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014 http://foggy.blogs.iva.co.uk