Construction & CIS Calculators

How these four tools fit together

Most guidance treats CIS, VAT and retention as separate topics. On a real construction invoice, they usually aren't — they happen on the same payment, in a fairly predictable order. This page groups the tools around that order, so you can move between them without hunting for the next one.

1. Verify and deduct. Before the first payment on a contract, a contractor verifies the subcontractor with HMRC, which sets the CIS rate — 20%, 30% or 0% for gross status. The CIS Deduction Calculator applies that rate to the labour element of the invoice, keeping materials out of the calculation.
2. Check the VAT treatment. If both parties are VAT-registered and the work falls under CIS, the domestic reverse charge often applies instead of normal VAT — meaning the subcontractor doesn't charge VAT on that invoice at all. The VAT Reverse Charge Checker confirms whether that applies and gives the wording to put on the invoice.
3. Account for retention. Many construction contracts withhold a percentage of each certified payment until practical completion, with a further slice held until the defects liability period ends. The Retention Calculator works out what's withheld and when it's due back.
4. Reconcile at year end. Because CIS is deducted at a flat rate regardless of a subcontractor's actual expenses or personal allowance, most subcontractors end up owed money back at Self Assessment. The CIS Refund Estimator gives a rough sense of whether that's likely and how much.

None of these tools file anything with HMRC on your behalf — they're worksheets to check your own numbers before you invoice, pay, or submit a return. Always confirm the final figures against HMRC's own guidance or your accountant, particularly on gross status changes or reverse charge edge cases.