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.
Mucka handles this without any new pages. You flag the clients you subbie for once, and from then on the payment screen captures the deduction every time.
One-off setup
Head to Settings → Subbie work 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.
When you raise the invoice
Mucka handles the awkward VAT bits for you:
- VAT is set to zero automatically. 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.
- 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 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
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.