CIS Deductions | TinyTax Support

CIS Deductions

How Construction Industry Scheme (CIS) deductions work on the CT600. Covers Box 515 and current limitations in TinyTax.

Does your company have CIS (Construction Industry Scheme) deductions? This guide explains what CIS means for your CT600 and the current limitations in TinyTax.

What Are CIS Deductions?

If your company works as a subcontractor in the construction industry, your clients (contractors) may deduct tax at source from your payments under the CIS. These deductions are a form of income tax paid on your behalf.

When filing your CT600, CIS deductions suffered should be reported in Box 515 (Income tax deducted from profits). This reduces your corporation tax liability — you've already paid tax through CIS, so you shouldn't pay it twice.

Does TinyTax Support CIS Deductions?

TinyTax does not currently have a dedicated CIS deduction field (Box 515).

This means you cannot claim CIS deductions suffered against your corporation tax bill through TinyTax. Your CT600 submission will not include the Box 515 element, so HMRC will not automatically offset your CIS deductions.

⚠ If your company has suffered significant CIS deductions, you may need to use specialist CT600 software or an accountant to ensure Box 515 is included in your return. Without it, you could overpay corporation tax.

What You CAN Do in TinyTax

While TinyTax can't report CIS deductions (Box 515), it can handle the rest of your CT600:

CIS Income

Enter your gross CIS income (before deductions) as Turnover (Box 145). This is the full contract value, not the net amount you received after CIS deductions.

CIS Costs

If your company also pays subcontractors under CIS:

  • Enter subcontractor costs in Cost of raw materials and consumables
  • CIS deductions you've made from subcontractor payments are a creditor (owed to HMRC)

Trial Balance Import

If you use accounting software (FreeAgent, Xero, Sage), the trial balance import maps CIS accounts automatically:

  • CIS income → Turnover
  • CIS labour/materials costs → Cost of raw materials and consumables
  • CIS deductions receivable → Current assets (balance sheet)
  • CIS deductions payable → Creditors (balance sheet)

How to Claim Your CIS Deductions

Since TinyTax can't include Box 515, you have two options:

Option 1: Use Specialist Software for the Full CT600

File your CT600 through software that supports Box 515 (TaxCalc, Taxfiler, etc.) to claim CIS deductions in the return itself.

Option 2: Claim from HMRC Separately

File your CT600 through TinyTax (without Box 515), then contact HMRC to claim the CIS deductions as a refund or offset. You can do this by:

  • Writing to HMRC's Corporation Tax office
  • Calling the CT helpline
  • Including details of CIS suffered (amounts, contractor names, deduction statements)
ℹ Keep all CIS deduction statements from your contractors. You'll need them whether claiming through your CT600 or directly from HMRC.

Common Questions

Q: If I file through TinyTax without Box 515, will I overpay tax? A: Your CT600 will calculate the correct corporation tax liability, but it won't offset the CIS you've already paid. You'll need to claim the CIS deductions separately from HMRC to avoid overpayment.

Q: Can I use Other adjustments as a workaround? A: No. Other adjustments change your taxable profit, which is different from claiming tax already paid. CIS deductions are a credit against your tax bill (Box 515), not a deduction from profits.

Q: My CIS deductions are only small — does it matter? A: If the amount is small and you're happy to claim it separately from HMRC, you can file through TinyTax and contact HMRC afterwards. For larger amounts, consider specialist software.

Q: Will TinyTax support CIS deductions in the future? A: It's on our radar. Contact us if this is important for your business — user feedback helps us prioritise features.

Still Have Questions?

If you need help with CIS-related filing, get in touch.

Last updated: February 2026

Was this guide helpful?