Tax Guide for Plumbers

A self-employed plumber earning the UK median of around £40,000 profit will pay approximately £5,486 in Income Tax and £2,194 in National Insurance for 2026-27 — a total of roughly £7,680. Your exact bill depends on your taxable profit after allowable expenses.

Here is how the 2026-27 rates work:

• Personal Allowance: The first £12,570 of profit is tax-free.
• Basic rate (20%): Profit between £12,570 and £50,270 is taxed at 20%.
• Higher rate (40%): Profit between £50,270 and £125,140 is taxed at 40%.
• Class 2 NI: £3.45/week (£179.40/year) — voluntary from April 2024, but paying preserves State Pension entitlement.
• Class 4 NI: 6% on profits between £12,570 and £50,270, then 2% above £50,270.

The more legitimate expenses you claim, the lower your taxable profit — and the less tax you pay. A plumber who tracks expenses carefully can easily save £1,500-£3,000 per year compared to one who does not.

Plumbers can claim a wide range of business expenses against their income, from tools and materials to van costs and insurance. If an expense is "wholly and exclusively" for business purposes, it is allowable.

The main categories of claimable expenses for plumbers include:

• Tools and equipment: Pipe cutters, wrenches, soldering kits, power tools, drain rods, inspection cameras.
• Materials: Copper pipe, fittings, sealant, solder — anything used on customer jobs.
• Van costs: Fuel, insurance, MOT, servicing, road tax. Choose between actual costs or HMRC's flat-rate mileage (45p/mile first 10,000 miles, 25p after).
• Insurance: Public liability, professional indemnity, tool cover, van insurance.
• Professional fees: Gas Safe registration, CIPHE membership, WaterSafe listing.
• Training: CPD courses, refresher training, unvented hot water qualifications.
• Admin: Phone, accounting software, bookkeeping fees, stationery.
• Marketing: Website, Checkatrade, Google Ads, business cards, branded clothing.

Keep every receipt. HMRC requires you to hold records for at least 5 years after the 31 January submission deadline. Digital photos of receipts are accepted — you do not need to keep paper originals.

Yes. A work van is one of the largest and most valuable tax deductions for a self-employed plumber. You have two options for claiming van costs, but you must pick one method and stick with it for the life of that vehicle.

Option 1 — Actual costs: Keep receipts for fuel, insurance, road tax, MOT, servicing, repairs, and parking. If you also use the van personally, reduce the claim by the personal use percentage (e.g. 80% business use = claim 80% of costs). If you buy the van outright, claim the purchase price through the Annual Investment Allowance (AIA), which allows 100% deduction in the year of purchase up to £1 million.

Option 2 — Simplified mileage: Use HMRC's flat rate of 45p per mile for the first 10,000 business miles, then 25p per mile after that. This covers all running costs — you cannot claim fuel, insurance, or servicing on top. You will need a mileage log recording each business journey.

For most plumbers covering 15,000-25,000 business miles per year, actual costs usually give a larger deduction than the flat rate. However, mileage is simpler and requires less record-keeping.

If you lease the van, monthly lease payments are fully deductible (reduced by personal use percentage). If you buy on HP, claim the capital element through AIA and the interest as a separate expense.

You must register for VAT if your taxable turnover exceeds £90,000 in any rolling 12-month period (2026-27 threshold). Below that threshold, registration is voluntary.

Most sole-trader plumbers turn over less than £90,000 and do not need to register. However, there are reasons you might choose to register voluntarily:

• Reclaiming VAT on purchases: If you buy expensive tools, a van, or large quantities of materials, you can reclaim the 20% VAT on those purchases.
• Credibility with commercial clients: Some commercial customers and main contractors prefer to work with VAT-registered subcontractors.

The downsides of voluntary registration: you must charge VAT on your invoices (making you 20% more expensive to non-VAT-registered customers), file quarterly VAT returns, and keep more detailed records.

If you are close to the threshold, consider the Flat Rate Scheme. Plumbers on the FRS pay a fixed percentage of gross turnover (currently 9.5% for "plumbing or heating") instead of calculating exact VAT on every transaction. This is simpler and can sometimes save money.

The Construction Industry Scheme (CIS) requires main contractors to deduct 20% tax at source from payments to unregistered subcontractors, or 30% if you are not registered with CIS at all. If you do any subcontract work for other contractors, CIS will affect you.

Here is how CIS works in practice:

• If you are CIS-registered and verified, the contractor deducts 20% from your labour payment and sends it directly to HMRC.
• If you are not registered, the deduction is 30%.
• If you have gross payment status, the contractor pays you in full with no deduction.

The deductions are not an extra tax — they are advance payments towards your Income Tax and NI bill. When you file your Self Assessment, the CIS deductions are credited against your liability. If too much was deducted, you get a refund.

To register for CIS, call the HMRC CIS helpline on 0300 200 3210 or register online at gov.uk. You will need your UTR and National Insurance number.

Important: CIS only applies to construction work done for contractors, not to work done directly for homeowners. If all your work is domestic, CIS does not apply.

The key Self Assessment deadlines are 31 October for paper returns and 31 January for online returns. Missing the 31 January deadline triggers an automatic £100 penalty — even if you owe no tax.

Here are all the dates you need to know:

• 5 April: Tax year ends. Your profit for the year running 6 April to 5 April is what you report.
• 5 October: Deadline to register for Self Assessment if this is your first year of self-employment (use form CWF1).
• 31 October: Deadline for paper tax returns (rarely used now).
• 31 January: Deadline to file your online return AND pay the tax owed for the previous year. Also the deadline for your first Payment on Account.
• 31 July: Second Payment on Account due.

Payments on Account: If your tax bill is over £1,000 and less than 80% of it was collected at source (e.g. through CIS), HMRC will ask you to make two advance payments towards next year's bill. Each payment is 50% of the previous year's liability. This catches many plumbers off guard in their second year of self-employment.