.Your first tax year of trading was 2013/14 so your first basis period is 1 October 2013 to 5 April 2014. Take a look here on calculating taxable profits.You need to enter the full accounting period figures in the self-employment pages SA103 which you can find here. The adjustment is calculated by dividing your post capital allowances profit by the number of days in your accounting period and multiplying the result by 178, the number of days from 6 April 2014 to 30 September inclusive. Put the resulting figure as a negative in box 68 of page SEF4 of the SA103 pages. If your post capital allowances profit was £36,000, then the figure to go in box 68 would be £17,556 (£36,000 / 365 x 178). That will leave £18,444 taxable in 2013/14.I hope this helps but let me know if you have any further questions.