CIS monthly return deadline: contractor compliance calendar for UK startups
Not every startup touches CIS. But if your UK company pays subcontractors for construction work, fit-outs, or certain property services, Construction Industry Scheme (CIS) rules apply. The monthly return deadline is fixed: the 19th of each month.
Miss it and HMRC penalties follow. Get it wrong and subcontractors complain about 30% deductions.
What is the CIS monthly return deadline?
The CIS monthly return deadline is the 19th of every month. Contractors must submit a CIS return to HMRC reporting payments to subcontractors and deductions made in the previous tax month.
The return is usually filed online (CIS300). Payment of deductions to HMRC follows CIS payment rules for the same period.
CIS monthly compliance flow
SYSTEM INSIGHT / NEXT STEP
Make the next move with clarity.
If this issue is already showing up in reporting, runway, or team decisions, the next move is usually clearer with a structured finance view.
Who needs to register for CIS?
Register as a contractor if your business pays subcontractors for:
Construction operations (building, alteration, repair, demolition)
Certain site preparation and cleaning services
Some property-related work caught by CIS rules
UK startups in proptech, facilities, or physical product installation sometimes trigger CIS unexpectedly. Check GOV.UK guidance or ask your accountant before first subcontract payment.
Subcontractors register separately and seek verification for reduced deduction rates.
Monthly CIS calendar (contractors)
When | Action |
Ongoing | Verify new subcontractors with HMRC |
When paying | Deduct CIS at 20% (registered) or 30% (unverified) |
By 19th each month | Submit CIS monthly return for previous tax month |
By payment due date | Pay CIS deductions to HMRC |
After filing | Provide payment statements to subcontractors |
The tax month runs 6th to 5th. The return due 19 May covers the tax month ending 5 May.
What goes on the monthly return?
The CIS return reports, for each subcontractor:
Gross amount paid
Materials costs (if excluded from deduction)
CIS tax deducted
Subcontractor UTR and verification status
Your bookkeeping system should tag CIS payments consistently. Reconstructing three months from bank statements is painful.
Penalties and common mistakes
Mistake | Consequence |
Missing the 19th deadline | HMRC late filing penalties |
Wrong verification status | 30% deduction disputes |
Mixing materials and labour | Incorrect deductions |
No payment statements | Subcontractor compliance issues |
CIS is operational, not annual. Treat it like payroll: monthly, non-negotiable.
CIS and startup finance ops
US-focused startup finance blogs rarely cover CIS. For UK companies with subcontract spend:
Build CIS into your month-end close
Separate subcontractor payments in Xero
Calendar the 19th before you hire project managers who onboard subs weekly
In practice
AccountUp runs compliance calendars alongside bookkeeping so CIS does not sit in a forgotten spreadsheet tab.
FAQs
When is the CIS monthly return due?
The CIS monthly return is due by the 19th of each month for the previous tax month (6th to 5th).
What is the difference between 20% and 30% CIS deduction?
20% typically applies to verified subcontractors registered with HMRC. 30% applies when verification fails or status is unknown.
Do SaaS startups need CIS?
Pure software businesses often do not. Companies paying for construction-related subcontract work may need to register as contractors.
Is CIS the same as VAT or PAYE?
No. CIS is a separate scheme for construction industry subcontractor payments. You may also run PAYE for employees and VAT if registered.
Can I file a nil CIS return?
Yes. If you made no payments to subcontractors in the tax month, file a nil return by the 19th anyway.
**Paying subcontractors and unsure about CIS?** Talk to an Expert.
