What it does
The S+ Money CIS Refund Calculator helps self-employed construction subcontractors paid under the Construction Industry Scheme (CIS) see whether they're likely to get tax back. Contractors take 20% (or 30% if you're not registered) off your labour before they pay you. That money is an advance payment towards your tax and National Insurance. Once your expenses and Personal Allowance are counted, many subbies have had too much taken and are owed a refund.
Ask in plain English, for example "I'm a CIS chippy, earned £32k gross last tax year with 20% taken, spent £1,200 on tools and drove 8,000 miles. What's my refund?". It works out:
- your taxable profit after allowable expenses (tools, van mileage at HMRC's flat rates, parking, phone, PPE, training, insurance, accountant), or the £1,000 trading allowance if that's better;
- income tax (England, Wales and Northern Ireland, or Scottish bands) and Class 4 National Insurance, plus your Class 2 position;
- the estimated refund or amount to pay against the CIS already deducted (and any PAYE tax on a second job), with the working line by line;
- the expenses subbies often miss, and whether payments on account are likely.
It covers tax years 2025-26 and 2026-27. Every rate comes from GOV.UK (checked 21 October 2026).
Tools
| Tool | What it does | Changes anything? |
|---|---|---|
estimate_cis_refund | Estimates the refund or amount owed from your gross CIS income, CIS deducted, expenses and any other income. Shows a result card. | No. Read-only. |
get_cis_tax_rates | Lists the rates and thresholds for the year with GOV.UK links. | No. Read-only. |
Using it
- ChatGPT: find "S+ Money CIS Refund Calculator" in the apps directory and connect it, then just ask about your CIS refund.
- Any MCP client: add the server URL
https://mcp.splusmoney.co.uk/mcp. No sign-in is needed. - On the web: use the same calculator at refund.splusmoney.co.uk.
What it can't do
- It gives an estimate, not tax advice. It doesn't see your HMRC record or file anything.
- It doesn't cover student loans, Marriage Allowance, pension or Gift Aid relief, savings, dividend or property income, losses, partnerships or limited companies.
- It never asks for your name, UTR, National Insurance number or bank details. Don't type them into a question for the tool.
Want it filed for you?
S+ Money prepares and files Self Assessment returns for CIS subcontractors. Use the "Let us file it for you" button on the result card or the web calculator.
Contact
Sovereign Plus Money Ltd (company registration in progress). Email hello@splusmoney.co.uk.