How to use this CIS Tax Deduction Calculator

This calculator helps you work out CIS deductions, VAT treatment, and final payments for UK construction invoices. Follow the steps below in order.

Step 1 Enter labour and materials

• Enter the Labour Amount (£) – CIS is calculated only on this amount

• Enter the Materials Cost (£) – materials are not subject to CIS

Step 2 Check the total invoice amount

• Total Invoice Amount (£) is calculated automatically

• It includes labour, materials, and VAT (if applicable)

• This field is read-only and cannot be edited

Step 3 Choose payment type

• Select Gross if the amount before CIS deduction is required

• Select Net if you want to calculate backwards from a net payment

Step 4 Select CIS status

Choose the subcontractor’s CIS status:

• Registered with HMRC – 20 percent CIS deduction

• Not registered – 30 percent CIS deduction

• Gross payment status – 0 percent CIS deduction

Step 5 Select VAT treatment

Choose how VAT applies to the invoice:

• Standard VAT applies – VAT at 20 percent is added to labour and materials

• Domestic Reverse Charge applies – VAT is not charged on the invoice

• Not VAT registered – no VAT is applied

A message below the selector will confirm which VAT treatment is in use.

Step 6 Click Calculate

• Press Calculate to generate the results

• The calculator will show:

  • CIS tax deducted

  • VAT amount

  • Net payment to subcontractor

  • Gross payment

Step 7 Recalculate if anything changes

• If you change any value after calculating, the calculator updates automatically

• The button text changes to Recalculate to show the figures were refreshed

Important notes

• CIS is always calculated only on labour, never on materials or VAT

• Domestic Reverse Charge means VAT is not included on the invoice

• This calculator is for guidance only and does not replace professional tax advice

This tool is designed to match real UK construction invoicing practice and works correctly on both desktop and mobile devices.