CIS subcontractor: how should I use a self-employed tax estimate?

If you work under CIS, this guide explains how to think about estimates and why deductions during the year can change the picture.

CIS deductions during the year are not the same as your final Self Assessment position.
Use an annual profit estimate for planning, then verify details on GOV.UK.
This site does not model every CIS specific rule; treat it as a baseline estimate.

What CIS changes

CIS often involves deductions from payments. That can affect how much has already been paid versus what your final calculation shows.

Enter annual profit after allowable expenses. If you track CIS deductions separately, keep them in your records rather than forcing them into profit.

Confusing deductions with tax due, or assuming deductions mean you do not need to file.

Not tax advice. This page is an educational guide. For official rules, verify the sources below.

Last updated: 2026-04-20

Does this calculator handle CIS deductions?

Not directly. It provides a self-employed baseline estimate from profit.

Can I still use it?

Yes, as a planning baseline, but verify CIS specifics using official guidance.

Where can I check what CIS is?

See GOV.UK overview of the Construction Industry Scheme.

For official rules and definitions, verify with the references below.