Your monthly CIS300 return

As a contractor you owe HMRC a CIS300 return every month, due by the 19th of the following month.

Go to Tax, then CIS, and choose a tax year. All twelve months are listed, including the quiet ones.

Nil returns are still due

Since 6 April 2026 a nil return is mandatory. A month in which you paid nobody still owes HMRC a return, and Kontala gives that its own status rather than leaving the row blank.

Month statuses

• Not started - the month has not begun.
• In progress - the month is running.
• Due - the month has ended and there are payments to report.
• Nil return due - the month has ended and nobody was paid.
• Overdue / Nil return overdue - past the 19th.
• Filed - you have recorded it as filed.
• Amendment needed - the payments in this month have changed since you filed.

Whole pounds

HMRC requires payments and materials in whole pounds, so Kontala truncates them. The deduction figures are exact.

Where the rounding actually bites, the return says how much has been dropped across it - because that is what explains a difference between this return, the statements you sent, and your CIS control account.

Missing details

If your Company Details are missing something HMRC's monthly return needs, the screen names it before the 19th rather than after. Add it on Company details.

Recording it as filed

Kontala does not send CIS300 returns to HMRC. File the return on HMRC's own service, then record it here:

1. Choose Mark as filed.
2. What you withheld moves onto the PAYE and CIS you owe HMRC.

The screen says Recorded as filed rather than "Filed", because it is your own record and not a receipt. Choose Not filed after all to undo it.

If the figures change afterwards

If payments in a filed month move, the row reads Amendment needed.

HMRC expects a corrected monthly return and a corrected statement for any subcontractor whose figures moved - a subcontractor holding a statement that disagrees with what HMRC was told cannot reclaim their deduction.

Send both, then choose Record the amendment. Nothing is blocked in the meantime: the month stays open to correction deliberately.

Downloads

Each month can be downloaded as a PDF or a CSV for keying into HMRC's service or handing to your accountant.

Related

• Payment and deduction statements
• Record your CIS role