Why Does My CT600 Show a Different Tax Amount to My Tax Calculation?

TinyTax calculates your corporation tax to the penny, but the CT600 form rounds the figure to the nearest pound for display. This guide explains why the two figures differ and which amount to pay.

Why the Two Figures Differ

Your Tax Computation shows the precise calculated amount — for example, £599.45. The CT600 PDF preview shows the same amount rounded to the nearest pound — for example, £599.

This display rounding is by design. The CT600 PDF is a presentation document — the actual XML filed with HMRC always contains the full figure to the penny.

Which Amount Do You Pay?

Pay the amount shown in your HMRC Business Tax Account — this reflects the precise figure HMRC received from the XML submission, including pence. You can check this by logging in at gov.uk/log-in-register-hmrc-online-services and going to Corporation Tax.

The rounded figure on the CT600 PDF is for display only and does not represent the amount HMRC has assessed.

How TinyTax Handles Rounding

• The XML submitted to HMRC contains the full precise figure (e.g. 599.45), as required by the CT600 schema.
• HMRC records and assesses the precise figure from the XML — the rounded display on the CT600 PDF does not affect what HMRC holds as your liability.
• The CT600 PDF that TinyTax generates shows the rounded figure for presentation purposes.
• The Tax Computation document shows the precise figure for your own records.

Common Questions

Is the rounding always up?

No — the CT600 PDF display rounds to the nearest pound. £9.49 rounds down to £9; £9.50 rounds up to £10. HMRC's record of your liability reflects the precise submitted amount, not the rounded CT600 display value.

Does the rounded figure affect my accounts?

The corporation tax charge in your statutory accounts should match the actual liability. If TinyTax auto-populates the Corporation Tax Payable figure in your balance sheet, it uses the precise calculated amount, not the rounded CT600 display figure.

What if HMRC shows a different amount in my Business Tax Account?

The HMRC Business Tax Account will typically show the precise amount from your XML submission, including pence — this is expected and correct. If the HMRC figure differs significantly from what TinyTax calculated (more than a few pence), check that your accounting period dates and submitted figures are correct. A difference of up to 50p is always display rounding on the CT600 PDF.