A guide to the various corporation tax rates over the past few years and an overview of the previous marginal relief calculation.
A freeview 'At a glance' guide.
Company tax rates

2015/16 to 2016/17  2014/15  2013/14  2012/13  2011/12  2010/11  
Rate  Profits £  Effective %  Effective %  Effective %  Effective %  Effective %  Effective %  Effective % 
Small  0  300,000  19  20  20  20  20  20  21 
Marginal  300,001  1,500,000  19  20  21.25  23.75  25  27.5  29.75 
Main  1,500,001 and above  19  20  21  23  24  26  28 
Fraction  n/a  n/a  1/400th  3/400ths  1/100th  3/200ths  7/400ths 
The company tax year starts on 1 April.
The main rate of company tax for all nonring fence profits is 19% for Financial Year 20172019.
Section 46 Finance Act 2016 set the CT rate for Financial Year 2020 as 17%. Prime Minister Johnson made a pregeneral election pledge to reverse this in November 2019 and the change is included in Finance Act 2020.
Finance Act 2021 provides that from April 2023, the main rate of Corporation Tax will increase to 25% for companies with chargeable profits over £250,000.
Companies (up to 2014/15): The marginal relief calculation
Marginal relief is given by:
(Upper limit – profits) x basic profits x fraction
profits
Upper and lower limits are reduced where:
Alternatively, you can calculate Corporation Tax on slices of profit using marginal rates:
Basic example
For a company with a 31^{st} March 2012 yearend and profits of £500,000 and no associated companies and no franked investment income, the marginal relief calculation is as follows:
Tax @ 26% on £500,000 = 130,000
Less:
Marginal relief
(1,500,000 – 500,000) x 3/200 = (15,000)
Tax due = 115,000
Alternatively, you can do this calculation as follows:
First 300,000 @ 20% = 60,000
Next £200,000 @ 27.5% = 55,000
Tax due = 115,000
What is the marginal rate?
If small company’s rate is 20% and the main rate is 26%
300,000 x 20% = 60,000
1500,000 x 26% = 390,000
1200,000 x X% = 330,000
330,000/1,200,000 =27.5% marginal rate
If small company’s rate is 20% and the main rate is 25%
300,000 x 20% = 60,000
1500,000 x 24% = 360,000
1200,000 x X% = 300,000
300,000/1,200,000 =25% marginal rate
What is the marginal rate fraction?
The difference between the main rate and the marginal rate expressed as a fraction.
So 29.75%  28% = 1.75% = 7/400
28.75%  27% = 1.75% = 7/400
27.5%  26% = 1.5% = 3/200
26.25%  25% = 1.25% = 1/80
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