Monthly returns must be submitted to HMRC by the 19th of each month for the previous tax month, detailing all payments to subcontractors.

Include subcontractor details such as name, Unique Taxpayer Reference (UTR), and payment amounts in each return.

Provide deduction statements to subcontractors within 14 days of the tax month-end, showing tax deducted and payment made.

Verify subcontractors with HMRC before the first payment to determine the correct deduction rate (0%, 20%, or 30%).

If no payments are made in a month, a nil return must still be submitted by the 19th to avoid penalties.

Keep records of all CIS deductions, payments, and verification checks for at least three years after the tax year ends.

Annual returns are required by 19th April following the tax year-end to reconcile monthly submissions and finalise deductions.

Penalties for late filing start at £100 for one day late, with additional charges for further delays up to £3,000.

File CIS returns online via HMRC's Government Gateway or through compatible accounting software like Xero or QuickBooks.

Update records promptly if subcontractor status changes, such as switching from net to gross payment, to ensure accurate future returns.