Capital Gains for long periods

So if there is a 15 months period from 1 jan 2014 to 31 march 2015, We obviously divide that up into 2 separate computations for corporation tax purposes. Now if there was a chargeable gain on lets say dec 2014 and then a chargeable loss in march 2015, wouldnt we count gain in first 12 months computation? and loss in the other computation that we have for 3 months period? Please could you clear that Thanks