Corporation tax rate for profit between £300,000 and £1,500,000

-Your Taxable Profit is £400,000
-Tax before marginal relief is therefore £104,000 (i.e. £400,000 x 26%)
-The upper limit of your Taxable Profit range is £1,500,000
-Deduct the Taxable Profit from the upper limit (i.e. £1,500,000 -£400,000)
-This leaves £1,100,000
-Divide the £1,100,000 by 200 = £5500
-Multiply this by 3 = £16500, which is your amount of marginal relief

Your corporation tax payable is therefore £87500 (i.e. tax of £104,000 less marginal relief of £16500).