Best Invoicing App for Plumbers UK 2026: Gas Safe Numbers, CIS Deductions and Certificate Attachments
Plumber invoicing has more moving parts than most trades. Gas work invoices need your Gas Safe number. CIS subcontractors must show the labour/materials split. CP12 landlord certificates need to be attached or referenced. Staged payments on larger jobs need deposit invoices and final invoices. Getting the paperwork right first time avoids payment delays and compliance headaches.
This guide compares the best invoicing apps for UK plumbers in 2026 — looking specifically at Gas Safe number fields, CIS deduction support, certificate attachment, and VAT handling. Whether you are a sole trader plumber, a heating engineer running a small team, or a gas and plumbing contractor on CIS, there is an option here for your situation.
Plumber Invoice Checklist
Every plumber invoice in the UK should include the following:
- Gas Safe registration number (required for any gas work)
- Business name and address
- Unique invoice number
- Description of work completed
- Labour and materials itemised separately (essential for CIS subcontractors)
- VAT at 20% if VAT registered, plus your VAT number
- Certificate number (CP12 landlord safety record or WIAPS water hygiene certificate where applicable)
- Staged payment breakdown if the job was split into deposit and final payment
- Payment terms — 7, 14 or 30 days from invoice date
Comparison: Best Invoicing Apps for Plumbers UK 2026
| App | Cost | Free Plan | Gas Safe Field | CIS Support | Cert Attachment | VAT |
|---|---|---|---|---|---|---|
| Sleepless Tradesman | Free + Pro | Yes | Manual note | Yes | Yes | Yes |
| Commusoft | £45-150/mo | No | Yes (dedicated) | No native | Yes (integrated) | Yes |
| Tradify | £39-49/mo | No | Manual | No | Yes | Yes |
| Powered Now | £19-89/mo | No | Yes | Basic | Yes (integrated) | Yes |
| ServiceM8 | £9-89/mo | No | Manual | No | Yes | Yes |
App Reviews
Sleepless Tradesman
Sleepless Tradesman offers free invoicing built for UK tradespeople, with a CIS invoice format that supports the labour and materials split subcontract plumbers need. You can send invoices with a card payment link so customers pay on the spot after you complete the job, which cuts the average time to get paid significantly. The homeowner marketplace also gives sole trader plumbers a way to pick up new local leads without paying per-lead fees.
The main limitation for gas engineers is that there is no dedicated Gas Safe number field — you need to add it via a custom note or footer on your invoice template. For most plumbers this is a minor workaround, but dedicated gas service businesses may prefer Commusoft or Powered Now for the native compliance fields.
Commusoft
Commusoft is purpose-built for the plumbing and gas sector, and it shows. There is a dedicated Gas Safe registration number field that appears on every invoice for gas work. CP12 landlord gas safety certificates are linked directly to the job and invoice, so landlords receive both documents together. The software maintains a boiler service history per property, which makes annual service reminders and renewal quotes straightforward.
The weakness is cost. At £45 to £150 per month, Commusoft is aimed at established plumbing businesses running multiple engineers rather than sole traders. If you are a one-person operation doing mainly domestic plumbing rather than dedicated gas servicing, you are likely paying for features you will not use.
Tradify
Tradify produces professional invoice templates and integrates with Xero for accounting. Adding materials and labour as separate line items is straightforward, which covers the basic CIS requirement in practice even without dedicated CIS support. The Xero integration is a genuine advantage for plumbers who already use Xero for their accounts — invoices sync automatically without re-entering data.
There is no dedicated Gas Safe registration number field, so you need to add it manually as a custom line item or footer text. There is also no native CIS deduction calculation — if you work under CIS as a subcontractor you will need to handle the deduction calculation yourself and present the result on the invoice. For plumbers who are VAT registered and on CIS, this means more manual work.
Powered Now
Powered Now is a UK-built job management and invoicing app designed specifically for gas engineers and plumbers. It includes a Gas Safe number field, gas certificate templates, and invoice formats built around the compliance requirements of gas work. The certificate and invoice workflow is integrated, which reduces the risk of sending an invoice without the required documentation.
The product is smaller than Commusoft or Tradify, and some users find the interface less polished. CIS support is described as basic — it handles the presentation but may require manual input for the deduction calculation. At £19 to £89 per month it is more accessible than Commusoft for sole traders, and the Gas Safe-focused features make it a strong choice for heating engineers doing mostly gas servicing.
ServiceM8
ServiceM8 has a clean invoicing workflow with strong materials tracking per job. You can log parts used on each job and they carry through to the invoice automatically, which saves time on itemisation for plumbers who use a lot of varied materials. The per-job pricing model at lower tiers can work out well for plumbers doing a modest volume of jobs per month.
ServiceM8 has no Gas Safe field and no CIS support. It is an Australian product adapted for the UK market, which shows in some of the compliance gaps. For plumbers who are not on CIS and do not do gas work, it is a capable option. For gas engineers or CIS subcontractors, the missing compliance features are a significant limitation.
CIS Invoicing for Plumbers: The Key Rules
If you work as a CIS subcontractor — doing plumbing work for a main contractor rather than directly for a homeowner — your invoices must follow specific rules. The Construction Industry Scheme requires that CIS deductions apply to the labour element of your invoice only, not to materials. Getting this right on your invoice protects you from disputes and ensures you are deducted the correct amount.
A correctly formatted CIS plumber invoice should show:
- Labour subtotal (e.g. £500)
- Materials subtotal (e.g. £200) — exempt from CIS deduction
- Gross total before deduction (e.g. £700)
- CIS deduction at 20% of labour only (e.g. £100)
- Net amount payable (e.g. £600)
Note that VAT, if you are VAT registered, is calculated on the gross amount before the CIS deduction. The CIS deduction is taken from the net payment — it is not a discount on the invoice total, it is an advance payment of tax withheld by the contractor. Your monthly CIS deduction statement from the contractor confirms the amounts deducted and you use these to offset your tax bill.
Verdict
For most UK plumbers in 2026, the choice comes down to what type of work you do. Gas engineers doing CP12 certificates and boiler services should look at Commusoft or Powered Now for their dedicated compliance features. CIS subcontract plumbers who need labour/materials split invoicing at no cost should start with Sleepless Tradesman. Established plumbing businesses with a team that already use Xero will find Tradify integrates cleanly. ServiceM8 suits general plumbers without gas or CIS requirements who want clean job management.
The free tier on Sleepless Tradesman makes it the lowest-risk starting point — you can invoice professionally, split labour and materials for CIS, and accept card payments without a monthly subscription until you are ready to scale.
Frequently Asked Questions
What should a plumber's invoice include in the UK?
A UK plumber's invoice should include: your business name and address, invoice number, date, description of work done, labour and materials itemised separately (essential for CIS deductions), VAT at 20% if registered, your VAT number, your Gas Safe registration number for any gas work, and the Gas Safety certificate reference where applicable. For CP12 landlord safety checks, include the certificate number on the invoice so landlords can cross-reference records. Payment terms should state when payment is due — 7, 14 or 30 days.
Do plumbers need to show Gas Safe numbers on invoices?
There is no legal requirement to display your Gas Safe registration number on every invoice, but it is strong best practice for any job involving gas appliances or pipework. Landlords and property managers often require it to maintain their compliance records. Including it also protects you — it demonstrates you are registered to do the work if the job is ever queried. Some plumbing invoice apps have a dedicated field for this; others require you to add it as a custom line.
How do I invoice for materials and labour separately as a plumber?
Separating materials from labour on your invoice is essential if you work as a CIS subcontractor — CIS deductions apply to labour only, not materials. Even if you are not on CIS, separating them is good practice: it makes quotes easier to verify, reduces disputes, and helps customers understand what they are paying for. In Sleepless Tradesman, Tradify and most job management apps, you can add multiple line items to an invoice — list each material item separately, then list labour as a separate line or lines.