TOOL 01CISESTIMATE / NOT ADVICE
For self-employed construction subcontractors. See roughly how much of your CIS deductions you could get back, or how much tax you may still owe, and which Self Assessment boxes the figures go in. Free, no sign-up, and nothing leaves your browser.
Quick answer: your CIS refund is the CIS deducted (plus any PAYE tax) minus the Income Tax, Class 4 National Insurance and student loan due on your profit. For example, in 2026/27 a subcontractor in England with £40,000 gross CIS pay, £6,400 deducted and £14,000 of expenses (including 8,000 miles at 55p) has £26,000 profit, owes £2,686.00 tax and £805.80 Class 4, and could get about £2,908.20 back. Source: GOV.UK.
| Form and box | What | Amount |
|---|
Box numbers are from HMRC's 2025 to 2026 paper forms: SA103S, SA103F, SA102, SA100. HMRC's online return asks the same questions with different screens.
For a basic-rate taxpayer in England, Wales or Northern Ireland, every £100 of allowable expenses cuts the bill by about £26 (20% Income Tax + 6% Class 4). Common ones in construction:
Sources: GOV.UK: expenses if you're self-employed (travel, clothing, training) · GOV.UK: simplified expenses, vehicles · working from home flat rates
| Rate or threshold | 2025/26 | 2026/27 |
|---|---|---|
| Personal Allowance | £12,570 | £12,570 |
| Basic rate 20% (England, Wales, NI), taxable income up to | £37,700 | £37,700 |
| Higher rate 40% up to / additional rate 45% above | £125,140 | £125,140 |
| Scotland: starter 19% up to (after allowance) | £2,827 | £3,967 |
| Scotland: basic 20% up to | £14,921 | £16,956 |
| Scotland: intermediate 21% up to | £31,092 | £31,092 |
| Scotland: higher 42% up to / advanced 45% up to / top 48% | £62,430 / £125,140 | £62,430 / £125,140 |
| Class 4 NI: 6% from / 2% above | £12,570 / £50,270 | £12,570 / £50,270 |
| Class 2: Small Profits Threshold / voluntary weekly rate | £6,845 / £3.50 | £7,105 / £3.65 |
| Mileage, cars and vans: first 10,000 / after | 45p / 25p | 55p / 25p |
| Student loan Plan 1 / 2 / 4 (9%) | £26,065 / £28,470 / £32,745 | £26,900 / £29,385 / £33,795 |
| Plan 5 (9%) / Postgraduate Loan (6%) | not yet due / £21,000 | £25,000 / £21,000 |
Sources: GOV.UK: Income Tax rates and allowances · GOV.UK: Scottish Income Tax · GOV.UK: NI rates and allowances · GOV.UK: self-employed National Insurance rates · GOV.UK: simplified expenses, vehicles · GOV.UK: increasing mileage rates (17 June 2026) · GOV.UK: repaying your student loan · GOV.UK: rates and thresholds 2025 to 2026 · 2026 to 2027
£40,000 gross on CIS statements (£32,000 labour, £8,000 materials), £6,400 deducted at 20% on the labour. 8,000 business miles in the van and £1,600 of tools, PPE, phone and insurance.
| Turnover (SA103S box 9) | £40,000.00 |
| Materials (box 11) | −£8,000.00 |
| Mileage 8,000 × 55p (box 12) | −£4,400.00 |
| Other expenses (boxes 13 to 19) | −£1,600.00 |
| Profit (box 31) | £26,000.00 |
| Income Tax: (£26,000 − £12,570) × 20% | £2,686.00 |
| Class 4 NI: (£26,000 − £12,570) × 6% | £805.80 |
| Class 2 NI (treated as paid, profit above £7,105) | £0.00 |
| Total due | £3,491.80 |
| CIS deducted (box 38) | −£6,400.00 |
| Estimated refund | £2,908.20 |
The same figures for someone living in Scotland give £2,646.33 Income Tax and a £2,947.87 refund. With £10,000 of wages and a Plan 1 student loan as well, the loan alone adds £1,359 (9% of £42,000 − £26,900), which matches GOV.UK's own example.
Sources: GOV.UK: Income Tax rates and allowances · GOV.UK: NI rates and allowances · GOV.UK: simplified expenses, vehicles · GOV.UK: repaying your student loan · GOV.UK: SA103S form and notes
It depends on your profit, not on how much was deducted. HMRC adds up the Income Tax and Class 4 National Insurance due on your profit (plus any student loan repayments), then takes off the CIS deductions on your statements and any tax paid through a job. If the deductions are more than the bill, the difference is refunded. Because CIS is taken at 20% of labour before expenses and before your Personal Allowance, many subcontractors with modest profits get money back. Use the estimator above with your own figures.
Source: GOV.UK: pay tax and claim back deductions
Sole traders and partners claim through their Self Assessment tax return after the tax year ends on 5 April. You can file online from 6 April; the online deadline for the 2025 to 2026 return is 31 January 2027 (paper: 31 October 2026). If you stop trading during the year you may be able to claim a refund earlier using HMRC's form for sole traders and partners. Limited companies reclaim CIS through their payroll (EPS), not through Self Assessment.
Source: GOV.UK: pay tax and claim back deductions · GOV.UK: Self Assessment deadlines
On the 2025 to 2026 Self-employment (short) page SA103S, CIS deductions go in box 38 and your gross income in box 9. On the full page SA103F they go in box 81, with turnover in box 15. Use SA103S if your turnover was below £90,000 and your affairs are simple. The 2026 to 2027 forms are not published yet, so box numbers could change.
Source: GOV.UK: SA103S form and notes · GOV.UK: SA103F form and notes
Gross. HMRC's notes say to include the full amount before CIS deductions in turnover (box 9 on SA103S), including the materials you charged for, and then claim the materials as an expense. The deductions themselves go in the CIS box.
Source: GOV.UK: SA103S form and notes
Using simplified expenses for a car or van: 55p a mile for the first 10,000 business miles in 2026 to 2027 (increased from 45p, backdated to 6 April 2026), then 25p a mile. For 2025 to 2026 it is 45p then 25p. You cannot use the flat rate for a vehicle you have already claimed capital allowances on, and once you use it for a vehicle you must keep using it.
Source: GOV.UK: simplified expenses, vehicles · GOV.UK: increasing mileage rates (17 June 2026)
Not if your profits are at or above the Small Profits Threshold (£6,845 for 2025 to 2026, £7,105 for 2026 to 2027): Class 2 is treated as paid, which protects your National Insurance record. Below that you pay nothing but can choose to pay voluntarily (£3.50 a week for 2025 to 2026, £3.65 a week for 2026 to 2027). Class 4 is 6% on profits between £12,570 and £50,270 and 2% above, in both years.
Source: GOV.UK: self-employed National Insurance rates · GOV.UK: NI rates and allowances
It can. If you file Self Assessment, HMRC works out student loan repayments on your total income for the year (self-employed profit plus any wages) and collects them through the return, after taking off anything your employer already deducted. That comes out of any refund. For example, on Plan 1 in 2026 to 2027 you repay 9% of income above £26,900.
Source: GOV.UK: repaying your student loan
Only if you owe £1,000 or more through Self Assessment and less than 80% of your tax was collected at source. CIS deductions count as tax collected at source, so many subcontractors do not have to make payments on account. If you do, each one is half of last year's bill, due 31 January and 31 July.
Source: GOV.UK: payments on account
The 2026 to 2027 Income Tax bands, Scottish bands, National Insurance rates and student loan thresholds used here are the ones GOV.UK publishes for 2026 to 2027. The 55p mileage rate has been announced and backdated, but the legislation was still going through Parliament when it was published, and the government will review mileage rates again at Budget 2026. The 2026 to 2027 tax return forms are not out yet. If you are in Making Tax Digital for Income Tax, you report through software rather than the SA103 pages.
Source: GOV.UK: Income Tax rates and allowances · GOV.UK: increasing mileage rates (17 June 2026) · GOV.UK: Making Tax Digital for Income Tax
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