27/08/2026
If you're a subcontractor who has just filed your first update, please check one thing. Did you record and submit what you invoiced or what you were paid?
A few subcontractors have come to me recently after filing their first MTD quarterly update in accounting software. They suspected the income figure filed was wrong and the tax calculated with it. It was, by 20%.
They had recorded sales based on money received into the bank rather than the amount on the sales invoice.
Under CIS most contractors deduct 20% tax at source and pay it over to HMRC, so the amount received into the bank is lower than the amount invoiced. Turnover was understated across the whole quarter.
Two things caused it. They were raising invoices outside of their accounting software, so the software had no record of gross invoice values or deductions. Then when the money arrived into the bank they didn't know how to record the full sale in the software and account for the CIS tax suffered.
There’s an easy fix. Raise all sales invoices in the accounting software you use. Most good ones have a CIS function that accounts for the tax correctly and puts it on your balance sheet until year end.
I expect to see a lot of this over the coming quarters. Subcontractors whose records went in once a year, prepared properly from invoices, are now moving into MTD and onto software they've never used, with no guidance on how CIS deductions should be treated.
Software isn't the problem. Software nobody has been shown how to set up correctly is the problem.
If you work under CIS, check how your deductions are being recorded before the next update is due rather than after four quarters have gone in incorrectly.
If you're not sure how to use the software and record your income accurately, get help now rather than after three more updates have gone in wrong.
If you want someone to check it before the next update drop me a message.
Yes, that’s me in a yellow hard hat holding a drill. It’s AI generated. You’re unlikely to see me in this get up as I’m rubbish at DIY, but I’m very good at tax returns and bookkeeping.