VAT for Plumbers in the UK: When to Register and What Changes

VAT is one of those things most plumbers ignore until it suddenly matters. You have a good year, the turnover creeps up, and one evening you realise you might have crossed the line a few months ago without noticing. Getting it wrong is expensive, because HMRC can ask for the VAT you should have charged even if you never actually charged it.

This guide covers when you have to register, what changes in how you price and invoice, and the bits of VAT that are specific to plumbing and heating work. It's general guidance, not tax advice. VAT has plenty of edge cases, so check anything that matters with GOV.UK or an accountant who works with trades.

The £90,000 Threshold

You must register for VAT if your VAT-taxable turnover goes over £90,000 in any rolling 12-month period, or if you expect it to go over £90,000 in the next 30 days alone. The current threshold and rules are on GOV.UK's VAT registration page.

Two things catch people out.

It's rolling, not your tax year. You don't wait until April to check. At the end of every month, add up your taxable turnover for the last 12 months. If it's over the threshold, you have 30 days to register.

It's turnover, not profit. If you take £95,000 in a year but £40,000 of it goes on boilers, copper and fittings, you're still over. Materials you pass on to customers count towards turnover when they're part of what you bill.

A simple habit that saves a lot of worry: keep a running 12-month total in a spreadsheet or your accounting app, and set yourself an alert at around £80,000 so you have time to plan rather than react.

Should You Register Voluntarily?

You can register before you hit the threshold. Whether that makes sense depends mostly on who your customers are.

• Mostly homeowners: registering early usually hurts. Homeowners can't reclaim VAT, so you either put your prices up by 20% or swallow the VAT yourself. Most domestic plumbers stay unregistered for as long as they legally can.
• Mostly builders, developers, letting agents or businesses: registering can help. Your VAT-registered customers can reclaim the VAT you charge, so it costs them nothing extra, and you can reclaim VAT on your van, tools and materials.
• Big tooling-up year: if you're about to buy a new van or a lot of kit, the VAT you can reclaim on it might tip the balance.

Being VAT registered can also make a small firm look more established to commercial clients. That's not a reason on its own, but it's a fair point if you're chasing that kind of work.

What Changes Once You're Registered

Your Prices

From your registration date you charge VAT, usually at the standard 20%, on your taxable work. The real question is whether you add it on top or absorb some of it.

For commercial customers, adding it on is normal and nobody blinks. For homeowners, a straight 20% jump is noticeable. Many plumbers use the change as a moment to review their pricing properly: tighten up call-out and hourly rates, stop underquoting small jobs, and price bigger installs so they still win work with VAT included. Always quote homeowners VAT-inclusive, because that's the number they'll compare.

Your Invoices

A VAT invoice needs certain details, including your VAT registration number, the invoice date, a unique invoice number, a description of the work, the VAT rate and the VAT amount. HMRC lists the full requirements on GOV.UK's VAT invoice guidance.

Making Tax Digital

Every VAT-registered business has to keep digital records and file VAT returns through software that works with Making Tax Digital (MTD). Paper records and typing figures into the HMRC website aren't enough. Most mainstream accounting apps handle this, and returns are usually quarterly.

Separately, Making Tax Digital for Income Tax is rolling out for sole traders and landlords, starting with those over £50,000 of qualifying income from April 2026 and dropping to £30,000 from April 2027. It's a different scheme from VAT, but if you're getting near the VAT threshold you're likely to be in scope, so it's worth sorting your bookkeeping once and properly.

Schemes That Can Make Life Easier

HMRC runs a few schemes that change how you work out what you owe.

• Flat Rate Scheme: you pay a fixed percentage of your VAT-inclusive turnover instead of working out VAT on every purchase. It's simpler, but if you spend very little on goods you may count as a "limited cost trader" and pay a higher rate. For plumbers who buy a lot of materials, it's often not the best deal. Run the numbers before you join.
• Cash Accounting Scheme: you pay VAT when your customer pays you, not when you send the invoice. Handy if you do jobs for builders who take 60 days to pay.
• Annual Accounting Scheme: one return a year with advance payments through the year. Useful if quarterly returns feel like a chore, less useful if your income swings a lot.

The details and eligibility rules for each are on GOV.UK, and an accountant can tell you in ten minutes which one suits your mix of work.

VAT Rules Specific to Plumbing and Heating

This is where plumbing gets more interesting than most trades.

The Domestic Reverse Charge

If you're VAT registered and you do construction work for another VAT-registered business that's also registered for the Construction Industry Scheme (CIS), and they're not the end user, the domestic reverse charge may apply. In that case you don't charge them VAT. Your invoice says the reverse charge applies, and your customer accounts for the VAT instead.

A common example: you do the first fix plumbing on a housing development as a subcontractor for a builder. The builder is selling the houses on, so they're not the end user, and the reverse charge applies. If you fit a bathroom directly for a homeowner, it doesn't. HMRC's domestic reverse charge guidance has flowcharts that make it clearer. Get this wrong on a big contract and it's a headache to unpick, so check before you invoice.

Energy-Saving Materials

In Great Britain, installing certain energy-saving materials in homes is currently zero-rated for VAT, until 31 March 2027. That includes things like air source and ground source heat pumps, solar panels and some insulation. Standard gas boilers are not included. If you're moving into heat pump work, check the energy-saving materials guidance carefully, including which parts of a job qualify and the rules for Northern Ireland.

New Builds and Other Special Cases

Some work on brand new homes can be zero-rated, and some conversions and renovations of long-empty homes can qualify for the reduced 5% rate. There are also reduced rates for certain grant-funded heating work for qualifying people. These have strict conditions and paperwork, so treat them as "ask first, then quote".

Common VAT Mistakes Plumbers Make

• Not checking the rolling 12-month total and registering months late
• Quoting homeowners a price without saying whether VAT is included
• Charging VAT on a job that should have been under the reverse charge, or the other way round
• Joining the Flat Rate Scheme without checking the limited cost trader rule
• Mixing personal and business spending on one card, which makes reclaiming VAT on purchases messy
• Forgetting that VAT you've collected isn't your money, then being short when the return is due

That last one bites a lot of first-year VAT payers. A separate savings pot where you move the VAT from every payment as it lands takes the stress out of quarter end.

A Quick Checklist

1. Track your rolling 12-month turnover every month
2. Set an alert well before the £90,000 threshold
3. Decide early whether voluntary registration suits your customers
4. Review your prices before you register, not after
5. Pick MTD-compatible accounting software
6. Check whether the reverse charge applies on every subcontract job
7. Confirm the VAT rate on any heat pump, solar or new build work before you quote
8. Put VAT aside as you're paid

Keeping the Admin Under Control

VAT is a good reminder that the paperwork side of a plumbing business grows faster than the plumbing. Once you're registered, every job needs clean records: who the customer is, what the work was, what you quoted and when you were paid.

That's partly why we built Slotby. It answers your calls when you're on a job, books the work and sends you a clear summary of each caller and what they need, which makes it easier to keep tidy records from the first ring. If you're thinking about the bigger picture of running the business, our guides on setting up a plumbing business in the UK and whether to hire staff are good next reads.