How much tax should a plumber set aside? Tax and allowable expenses for 2025/26
A plumber's income is lumpy: a boiler install in one week, three small repairs in the next, and a stack of parts invoices in between. The tax is a simple share of the year's profit, so the job is to know that share early.
What the tax looks like
Using the 2025/26 rates (England, Wales or Northern Ireland, no other income), a plumber with £48,000 of takings and £9,000 of allowable costs has £39,000 of profit and about £6,872 of income tax and Class 4 National Insurance for the year, roughly £573 a month. The figures are an illustration, not an average for the trade. Tax is on profit, not takings.
| Profit for the year | Income tax + Class 4 NI | Per month | Per £1 of profit |
|---|---|---|---|
| £23,000 | £2,711.80 | £226 | 12p |
| £39,000 | £6,871.80 | £573 | 18p |
| £58,000 | £13,048.60 | £1,087 | 22p |
Open the calculator already filled in with this example and change the two numbers to yours. It also shows the January and July payment dates.
Costs a plumber usually claims
Claim only what you actually spent on the business, and only the business share of anything you also use personally.
- Parts and materials bought for jobs: pipe, fittings, valves, flux, solder. Keep supplier invoices, not just card statements.
- Tools and equipment: press tools, pipe benders, drain cameras. Small tools are usually costs for the year; large items can be handled as capital allowances (an accountant or the SA103 notes cover this).
- Van running costs: fuel, insurance, MOT and repairs on actual costs, or the flat mileage rate. Not both.
- Workwear and PPE: boots, gloves, overalls and protective gear. Everyday clothes don't count.
- Insurance and registration: public liability cover and the scheme fees needed to do regulated work, such as gas work.
- Training directly related to the work you already do, and trade body subscriptions.
The general list is on GOV.UK: self-employed expenses you can claim, and what you can't. If your costs for the year are under £1,000, the trading allowance may leave you less tax.
If you work through the Construction Industry Scheme
If a contractor pays you under CIS, they take a deduction before they pay you: 20% if you're registered, 30% if you're not, and nothing if you have gross payment status. GOV.UK says the deductions count as advance payments towards your tax and National Insurance bill, so they come off what you owe, and you get a refund if they added up to more than the bill. The percentage isn't applied to the whole invoice. GOV.UK lists items that come off the invoice first, including VAT, materials you paid for directly, fuel (except for travelling) and plant hire, so show them as separate lines on your invoices. Treat the deductions as tax already paid, not as a reason to skip the set-aside: check the figure against the calculator's profit figure in January.
VAT
If your taxable turnover goes over £90,000 in a 12-month period you must register for VAT. Parts and labour are both part of that turnover.
Records worth keeping
- Invoice every job with parts as a separate line. It matters for CIS and for your own profit per job.
- Keep the trade counter receipt, not just the bank line. One 'Screwfix, £212' covers a lot of different things.
- Log van miles by journey if you use the flat rate (date, from, to, miles).
- Note the CIS deduction from each payment statement, then total them for the year.
Plumbers who invoice jobs, pay for parts and run a van can use it for the sort-by-return-box layout: the SortedDesk Self Assessment Spreadsheet is a one-off £4.99 download for Excel and Google Sheets. It is a spreadsheet only: nothing here files anything with HMRC, and the sheet doesn't replace an accountant if your case is complicated.
Dates matter too: the 2025/26 return and tax are due on 31 January 2027, and payments on account can make that January bigger than the year's bill.
This is a planning guide, not tax advice. Figures worked with the calculator's 2025/26 rules, and GOV.UK sources read on 21 October 2026: Expenses if you're self-employed, CIS: make deductions and pay subcontractors, Simplified expenses: vehicles, When to register for VAT.
Try the calculator with this example