The HMRC CIS online service is the Government Gateway portal through which contractors carry out their core CIS obligations: verifying subcontractors, filing monthly CIS300 returns and viewing their CIS account.
The service is accessed through the HMRC online services portal at gov.uk using a Government Gateway user ID and password. Contractors must be registered for CIS before they can use it. The main functions are:
- Subcontractor verification. Before paying a subcontractor for the first time (or when verification status has lapsed), the contractor enters the subcontractor's UTR and name (and company registration number for limited companies). HMRC returns the correct deduction rate: 0% (Gross Payment Status), 20% (registered) or 30% (unregistered). The service also returns a verification number, which the contractor must record and include on the payment and deduction statement.
- CIS300 monthly return filing. The contractor submits details of every subcontractor paid in the tax month (payments, materials split, deductions made and verification reference). The return must be filed by the 19th of the following tax month.
- Nil return filing. If no subcontractors were paid in a month, a nil return must still be filed from April 2026 (reinstated obligation).
- Account view. Contractors can review previous returns and check payment records.
The CIS online service does not handle Gross Payment Status applications directly: those are made by contacting HMRC on the CIS helpline (0300 200 3210, Monday to Friday, 8am to 6pm) or in writing. From April 2026 the service feeds directly into HMRC's fraud-detection work: the "should have known" standard in Finance Act 2026 expects contractors to use it as a due-diligence step before every payment, not just on first engagement.
For a full walkthrough of contractor monthly obligations see CIS for contractors: your monthly responsibilities and how to verify subcontractors under CIS.