Free tools that use the real filing engine.
Not marketing approximations. These calculators run the same code that prepares an actual WrenTax filing — so what you see here is what a return would say. No account, no email, no catch.
Corporation tax calculator
Marginal relief, short periods, straddling financial years and associated companies — computed by the exact engine WrenTax files with, so the tool can't disagree with the return.
Open toolFirst-year Corporation Tax split
A first period over 12 months splits into two CT600s. See both returns, both deadlines and both payment references — the first-year split most free calculators skip.
Open toolCompany deadline calculator
One incorporation date in, every first-year deadline out — accounts, CT600, the Corporation Tax payment and your first confirmation statement, including the 21-month rule.
Open toolMarginal relief calculator
How the taper between the 19% and 25% rates really works across the £50k–£250k band, with the 3/200 formula, a worked example and a live calculator.
Open toolAssociated companies
Each associated company divides your £50k and £250k profit limits — so a 'small' company can pay 25%. Set the number and watch the thresholds move.
Open toolStraddling financial years
When your accounting period spans 1 April it splits across two Corporation Tax financial years. A worked example from the real engine — the split most free calculators skip.
Open toolDividend tax calculator
Salary and dividends stacked correctly for 2026/27 — income tax, employee National Insurance and dividend tax — to show your real take-home and the tax-efficient salary.
Open toolOptimal director salary
Don't just assert £12,570 — we run each candidate salary through the real Corporation Tax engine (employer NI, CT relief, dividend tax) and show which leaves you with the most.
Open toolVAT registration threshold
The threshold is £90,000 of taxable turnover in any rolling 12 months. Check where you stand, when you'd have to register, and the 30-day forward-look test that catches people out.
Open toolIs my company dormant?
'Dormant' has a strict legal meaning and a single transaction — even bank interest — can break it. Answer a few questions to see where you stand at Companies House and HMRC.
Open toolConfirmation statement due date
Enter your incorporation or last-statement date to get your confirmation statement (CS01) deadline, the £50 fee, and what it covers after identity verification.
Open toolLate filing penalty calculator
Enter your due date and when you expect to file. See exactly what Companies House will charge for late accounts, and the parallel penalty HMRC adds for a late CT600.
Open toolCompany deadline checker
Look up any UK company by number and see every statutory deadline — accounts, CT600 and confirmation statement — straight from the register. Free, no account, and subscribable as an iCal feed.
Open toolPrefer the explanation first?
Every guide, in plain English.
Dormant accounts, your first CT600, HMRC error 1046, the confirmation statement and every deadline — written by the people who built the engine behind these tools.
Read the guides