What it does
The S+ CIS Calculator helps UK construction contractors who pay subcontractors under the Construction Industry Scheme (CIS) understand their risk. Ask it in plain English, for example "I pay 15 subbies about £12k a week and two returns went in late. What's my CIS exposure?", and it works out:
- Late-return penalties for CIS300 monthly returns filed after the 19th (£100, then £200 at 2 months, then £300 or 5% at 6 and 12 months).
- Wrong-rate deduction cost: what HMRC can recover if unverified subcontractors were paid at 20% or 0% instead of 30%.
- April 2026 fraud rules, worst case: the Finance Act 2026 s.220 charge on labour bought through intermediaries, including directors' personal liability and the 5-year gross payment status bar.
It also explains CIS deadlines, rates, nil returns and the right to work checks for self-employed subcontractors from 1 October 2026. Every figure comes with its GOV.UK, HMRC or legislation.gov.uk source link.
Tools
| Tool | What it does | Changes anything? |
|---|---|---|
estimate_cis_exposure | Estimates yearly CIS exposure from your answers and shows a result card. | No, read-only |
cis_deadlines_and_penalties | Explains CIS rules, deadlines, penalties and the 2026 changes, with sources. | No, read-only |
get_cis_check_contact | Gives Sovereign Plus's phone, email and hours if you want your position checked. | No: nothing is sent, you contact S+ yourself |
How to use it
In ChatGPT
Open the ChatGPT plugin directory, search for S+ CIS Calculator and add it. Then start a chat and ask about your CIS position, or type @ and choose it.
In Claude
Open Customize → Connectors, find S+ CIS Calculator in the directory and connect it. No account or sign-in is needed.
https://mcp.sovereignplus.com/mcpThings to try
- "I pay 15 subbies about £12k a week and 2 returns went in late. What's my CIS exposure?"
- "8 of my 20 subcontractors aren't verified and I take 20% off them. How much could HMRC come after me for?"
- "When is the CIS return due and what's the penalty if I'm late?"
- "What changed in CIS in April 2026?"
- "Who can check my CIS is right?"
What it can't do
- It gives estimates, not tax advice. It does not see your HMRC records, and penalties can be reduced, waived or appealed.
- It is for UK contractors under CIS. It is not built for subcontractors working out their own tax, for PAYE or umbrella payroll, or for countries outside the UK.
- It does not file returns, verify subcontractors, contact HMRC, or send your details to anyone.
- It needs no account, and you should not give it names, UTRs, National Insurance numbers or bank details. It never asks for them.
Support
Email info@sovereignplus.com or call 023 9280 0686, Monday to Friday, 9am to 5pm (UK time).
To report a wrong figure or a broken source link, email us with the question you asked and the answer you got. We aim to reply within 2 working days.
Published by Sovereign Plus Solutions Ltd (Sovereign Plus (S+)), a UK CIS bureau. Website: sovereignplus.com. See also our privacy policy and terms of use.