My fees are paid in January but the tax years runs from April – April

So if you paid £250 on 1st Jan 2015 then the entire amount falls into the 2014-15 tax year (as it was paid between 6 April 2014 and 5 April 2015) and you do not need to do any calculations. If £350 was paid on 1st Jan 2016 then the entire amount falls into 2015-16. You do not need to take daily rates or pro-rata any expenses – all that matters is the date that the payment was made.