Corporate tax software exists because of one requirement: HMRC wants the computation and the accounts tagged in iXBRL, and no ordinary document tool produces that. Whether a company needs to buy any depends almost entirely on whether HMRC's free service covers its circumstances, and for a large share of small companies it does.
What the software has to produce
A CT600 with the correct supplementary pages, a corporation tax computation and a set of statutory accounts, the latter two tagged in iXBRL so HMRC's systems can read each figure. It also has to carry forward the pool balances, the losses and the loans to participators position from one year to the next, which is the part that matters more than the filing itself: a company that changes software mid-stream and loses its brought-forward figures has created a real problem.
When HMRC's free service is enough
HMRC provides a combined accounts and tax return service for companies with straightforward affairs, and straightforward means what it says: a single trade, no complications in the accounts, and a company that fits the small company reporting regime. A company with a group relationship, a chargeable gain, an R&D claim or a property portfolio will generally fall outside it, and the boundary is published rather than a matter of judgement.
What filing yourself gives up
The software checks arithmetic and format; it does not ask whether the company has claimed the capital allowances it is entitled to, whether the associated companies count is right, or whether last year's loss is being used in the best order. Those are the questions that move the number, and they are the reason most companies buy the filing and the thinking together. This site keeps a record of what the firms doing the thinking publish about their fees, which for seven out of ten is nothing.
Questions people ask about corporate tax software
Do I need corporate tax software?
Only if HMRC's free service does not cover your company. It is aimed at companies with straightforward affairs; a group, a chargeable gain, an R&D claim or a property portfolio generally falls outside it.
What format does HMRC require?
The return is filed online with the computation and the accounts tagged in iXBRL, which is why an ordinary document cannot be submitted.
What does software not do?
It does not tell you whether a relief has been missed, whether the associated companies count is right, or how best to use a loss. Those are judgements rather than arithmetic.