If you sometimes work as a subcontractor for another building business (typical on commercial jobs), they're required to deduct CIS tax from your invoice before paying you, and send that tax straight to HMRC. The money you never see still counts towards your tax bill at year end, so it's worth tracking accurately.
You flag the clients you subbie for once, and from then on the payment screen captures the deduction every time. One page adds it all up for the tax year.
One-off setup
Head to Settings → Money → Tax & subcontracting and enter:
- Your UTR (Unique Taxpayer Reference, 10 digits, on letters from HMRC)
- Your CIS verification status — gross (0%), standard 20% or higher 30%. If you're not sure, contractors default to deducting 30% until HMRC verifies you.
You only need to do this once. Mucka uses the rate to pre-fill payments so you don't have to maths each time.
Flag the contractor
Open any commercial client who pays you as a subcontractor, and tick I work for them as a subcontractor (CIS applies). From now on, new jobs for that client default to subbie work.
The toggle only shows on commercial clients — residential customers never deduct CIS.
Per-job override
A flagged client might use you as a normal supplier for some jobs and as a subbie for others. Open the job and the Subbie work tick is there to flip on or off. Whatever's set on the job carries through to the invoice.
The tick shows up whenever the client you've picked is one you subbie for — however you got to the job. Booked on the phone, converted from a quote, imported from a spreadsheet, made recurring, or set up by asking Mucka out loud: they all read the client's flag.
Invoices raised without a job
Not every invoice hangs off a diary entry. Raise one straight against a flagged client and it's still subbie work — the invoice screen shows the labour/materials split and the CIS figures as soon as you pick the client, and if you're VAT registered VAT goes to zero and the reverse-charge clause prints. Same for a stage invoice off a quote, a plot on a site, and the draft Mucka prepares for you when a job's finished.
When you raise the invoice
Mucka handles the awkward VAT bits for you:
- VAT is set to zero automatically — if you're VAT registered. UK construction subcontracting between VAT-registered businesses uses the domestic reverse charge — the contractor (the customer) accounts for VAT to HMRC, not you. Mucka sets VAT to 0 and prints the official reverse-charge clause on the PDF.
- Not VAT registered? Then there's no VAT on your invoices to begin with, and no reverse charge either — so Mucka leaves the clause off. The CIS panel and the labour/materials split still print, because CIS applies whatever your VAT position. Whether you're registered is the We are VAT registered switch in Settings → Business → Details.
- Tag each line as labour or materials. A small toggle appears under each line item. Mucka uses this so CIS deducts on the labour portion only at payment time (the HMRC rule). New lines default to Labour which covers most subbie work.
If you're VAT registered and your contractor is unusual and has confirmed in writing they're the end consumer (e.g. property developer keeping the build), tick the End-user exception box. VAT goes back to your normal rate; CIS still applies.
Recording the payment
When a subbie-flagged invoice gets settled, the payment screen swaps the usual single amount field for three:
- Gross amount settled — the full invoice amount being paid
- CIS deducted — pre-filled at your rate against the labour portion of this invoice (so a job that's 80% labour / 20% parts gets the right number out of the box). Override if the contractor used a different rate.
- Net received in your bank — auto-calculated, this is what actually hits your account
Save and the invoice marks paid as normal. The CIS amount is logged for the report.
See the running total
Reports → CIS suffered shows the lot for the current UK tax year (6 April to 5 April):
- Total CIS suffered
- Gross invoiced vs net received
- Breakdown per contractor, who you've subbied for and how much each one withheld
- A CSV export to hand to your accountant
On a phone with the new look, it's in the Menu under Finance as CIS taken off you (your accountant calls it CIS suffered; it's the same thing). The row shows once you've added your UTR or CIS status, or recorded a payment with CIS taken off. Tap the tax year at the top to pick another year. The card at the top shows the total taken off, what the work came to, and how much reached you against how much went to HMRC. Export for your accountant opens your phone's share sheet, so you can save the file or send it by email or WhatsApp. Your UTR and CIS status sit under it, with Subbie settings to change them, then each contractor with what they took off.
Or just ask Mucka — "how much CIS have I suffered this year" — and you'll get the headline number plus a pointer to the report.
Reclaiming it
The total goes on your Self Assessment SA103 (self-employment) or your Limited Company CT600 against your tax bill. If you've had more CIS deducted than you actually owe in tax, HMRC refunds the difference. Your accountant enters the numbers — give them the CSV export and they handle the rest.
What Mucka doesn't do (yet)
- Submit CIS300 returns to HMRC. That's the contractor's job (the business paying you), not yours.
- Verify you with HMRC. Your contractor verifies you via the CIS online portal, then tells you whether to put 20% or 30% on your status.
- Pay subbies of your own. If you also pay subcontractors, a separate skill is coming for that side.