Free tools
Free UK Corporation Tax tools
Free calculators for directors of UK limited companies: work out your Corporation Tax deadlines and other company tax figures in a minute, with the rules explained and linked to GOV.UK. They work on this site, inside AI assistants and on your own website.
Which free Corporation Tax calculators does Taxley offer?
Taxley's free calculators answer the Corporation Tax questions that directors of small UK companies ask most. Each one is listed below with what it works out. Every calculator shows a worked example, explains the rules with links to GOV.UK and gives you a link to your own result to save or share.
Corporation Tax calculator
Estimates the Corporation Tax a UK limited company pays on its taxable profits for one accounting period of up to 12 months. Applies the small profits rate, the main rate and marginal relief, with associated companies, short periods and periods that straddle 1 April. A close investment-holding company pays the main rate on all its profits. Returns the tax, the effective rate and the payment and filing dates.
Corporation Tax deadline calculator
Works out a UK private limited company's Corporation Tax payment date, CT600 filing deadline and Companies House accounts deadline from its accounting period. Accounts longer than 12 months are split into two Corporation Tax periods, each with its own payment date.
Corporation Tax late filing penalty and interest calculator
Works out HMRC's penalties for filing a UK company's Company Tax Return (CT600) late — the flat £200/£400 penalties, doubled for filing deadlines from 1 April 2026, and the 10% or 20% tax-geared penalty — plus late payment interest on the Corporation Tax at HMRC's published rates.
Open the calculator: Corporation Tax late filing penalty and interest calculator
Director's loan s.455 tax calculator
Works out the section 455 tax a UK close company owes on a director's or shareholder's loan still owed at the end of its accounting period, the relief for any part repaid within 9 months, the net tax and its due date. Uses the rate for the date the loan was made, including 35.75% from 6 April 2026.
Capital allowances calculator for companies
Works out a UK limited company's capital allowances for one accounting period: the annual investment allowance, full expensing, the 50% and zero-emission car first-year allowances, and writing-down allowances at 14% (18% before 1 April 2026, a hybrid rate for a period spanning that date) and 6%. It also shows balancing charges and the pools carried forward.
Open the calculator: Capital allowances calculator for companies
Chargeable gains calculator for companies (with indexation)
Works out a UK limited company's chargeable gain or allowable loss when it sells UK land or buildings, or shares it bought in one purchase, including indexation allowance frozen at December 2017. It shows the Retail Prices Index figures and factor used, and applies the rule that indexation can't create or increase a loss.
Open the calculator: Chargeable gains calculator for companies (with indexation)
Micro-entity and small company size checker
Checks whether a UK private company is a micro-entity, small, or neither for a financial year under the Companies Act 2006, using the limits raised for years starting on or after 6 April 2025, the 2-of-3 test, turnover pro-rating for short or long years, and the two-consecutive-years rule.
Open the calculator: Micro-entity and small company size checker
Long accounting period calculator: two CT600s
Splits UK company accounts covering more than 12 months (up to 18) into the two Corporation Tax accounting periods, with each period's dates, days, payment deadline and share of the profit by days, plus the CT600 filing deadline for both returns and the Companies House accounts deadline.
Open the calculator: Long accounting period calculator: two CT600s
iXBRL accounts checker
Upload a company's iXBRL accounts or Corporation Tax computations file (.html or .xhtml) and get a plain-English list of any problems: file safety, iXBRL structure and, when available, full validation against the taxonomy it names. The file is checked and then deleted. Web page only, because it needs a file upload.
Can AI assistants use these tools?
Yes. Assistants such as Claude and ChatGPT can call the calculators through Taxley's free Model Context Protocol (MCP) server, and developers can use the JSON API. Both give the same figures as these pages, with a link to the result, and need no key or account. The developer page explains how to set them up.
Add https://taxley.co.uk/mcp as a custom connector in your assistant, or read Taxley tools for developers and AI assistants for the steps, the API and the embed code.
Are the calculators free to embed on my website?
Yes. Each calculator that doesn't need a file upload has an embed version you can place on your own website with a short snippet, free of charge. Please keep the plain "Powered by Taxley" link that comes with the snippet, so your readers can see where the figures come from and check the full rules.
Copy the snippet from the embed section of the developer page. The calculator works on phones and without JavaScript.
Frequently asked questions
Are Taxley's calculators really free?
Yes. The calculators, the embeds, the JSON API and the MCP server are free to use, with no account and no key. We only ask that you link to taxley.co.uk when you publish a result, so readers can see how it was worked out.
Does Taxley save the figures I enter?
No. The figures you enter are used to work out the answer and are not saved to an account or a database. A result link simply carries your inputs in the web address, so anyone you share it with sees the same result.
Is a calculator result tax advice?
No. The calculators give general guidance based on the rules HMRC and Companies House publish on GOV.UK. They can't see your company's full circumstances, so check the figures against your own records before you file or pay.
How are the calculators kept accurate?
Each calculator applies the published rules to the figures you enter and says what it doesn't cover. We check the rules against GOV.UK, show the date of the last review on each page and link to every source, so you can follow each step yourself.
Can I file my Company Tax Return with Taxley?
Yes. Taxley is software for directors of small limited companies to prepare their CT600 and iXBRL accounts, file the return to HMRC and file the accounts at Companies House. Preparing and previewing a return is free; you pay one fee when you choose to file.
Last reviewed . The calculators give general guidance, not tax advice.