About Company Tax Helper

A free tool for directors of small UK limited companies. It turns your year's figures into a Corporation Tax estimate, the CT600 box figures and a salary and dividend plan.

What it is, and isn't

• It's guidance. It turns your figures into an estimate of the company's Corporation Tax, the CT600 box figures, deadlines and a salary and dividend illustration, using the rates in force for your dates.
• It's not tax, accounting, legal or financial advice. We're not accountants or tax advisers, the site isn't regulated, and using it doesn't make us your adviser. It can't know everything about your company.
• It's not HMRC, Companies House or GOV.UK and has no connection with them.
• It doesn't file anything or prepare statutory accounts. The company's directors are responsible for its accounts, its Company Tax Return and paying the right tax on time, whoever prepares them.
• The salary and dividend planner is an illustration under simple assumptions, not a recommendation. Personal circumstances such as other income, pensions, student loans, Scottish tax rates or IR35 can change the answer.
• Reading invoices, receipts and bank statements is automatic and can be wrong. Check every figure it finds before you rely on it.
• If you're unsure, ask a qualified accountant or tax adviser, or HMRC.

Your privacy

Everything is worked out in your browser. Your answers are saved only on your device (in your browser's local storage) so you can come back to them. They're never sent to us or anyone else. Invoices and receipts you upload are read inside your browser too: the files aren't uploaded anywhere, and only the figures we find are saved on your device. Use "Clear my answers" to delete them, and on a shared computer clear them when you've finished. We never ask for your HMRC, Government Gateway or Companies House login. If any site or email asks you to type it anywhere other than gov.uk, don't.

• Uploaded paperwork: invoices, receipts and bank statements are read inside your browser. The files aren't sent to us or anyone else. Only the figures found (dates, amounts, names and descriptions) are saved, in this browser on this device. "Remove all paperwork" deletes them.
• Reading software: the first time you upload a PDF or photo, your browser downloads free open-source reading software (pdf.js and Tesseract) from public code libraries (cdnjs.cloudflare.com, cdn.jsdelivr.net and tessdata.projectnaptha.com). Like any website, those servers see your IP address. They don't receive your files or figures.
• Hosting: Cloudflare hosts the site and keeps standard technical logs (such as IP addresses) for security and to count visits.
• Local storage: the site itself uses your browser's local storage only to remember your answers, your paperwork figures and your light or dark choice.

Advertising and cookies

The site is free because it shows ads from Google AdSense. Google and its partners may use cookies or similar technology to show ads, measure them and limit how often you see the same one. Where the law requires it, Google's consent message asks for your permission first, and you can choose non-personalised ads or change your choice later from the privacy settings button the message adds to the page. Ads never see your figures or the paperwork you upload.

• How Google uses information from sites that use its services
• Google ad settings: turn off personalised ads

Where the figures come from

• GOV.UK: Corporation Tax rates and marginal relief
• HMRC: CT600 (2026) Version 3 for the box numbers
• HMRC: main rate writing down allowance cut to 14% from 1 April 2026 and the hybrid rate
• GOV.UK: rates and thresholds for employers 2026 to 2027
• GOV.UK: tax on dividends
• GOV.UK: Corporation Tax late filing penalties

Every rate is checked against GOV.UK, and the calculator is tested against hand-worked examples before any change goes live.

What it doesn't cover

• Capital gains, R&D relief, group relief, creative reliefs and patent box
• Carrying losses back, or setting them against other income of the same period
• Full expensing, the 40% first-year allowance, structures and buildings allowance and long-life assets
• Loans to directors (s455 tax), close company rules and large-company instalment payments
• Northern Ireland Corporation Tax, ring fence trades and overseas income
• Charities, CICs taxed differently, and investment companies' management expenses

If any of these apply, the estimate won't be complete. Ask an accountant.

Found a mistake?

Tax rules have a lot of detail. If something here disagrees with GOV.UK, HMRC or your filing software, trust them over this site. Rates and forms are checked against GOV.UK every week, but changes can take a few days to appear here.