Contracting VAT problems are almost never about the rate — they’re about timing. Advance payments generally trigger VAT when received, not when work is done; retention has its own rules tied to certification and invoicing.
The classic failure: an advance lands in the bank, no tax invoice is raised, and the VAT surfaces months later in an assessment — with penalties.
The fix is procedural: every cash receipt gets classified the day it arrives — advance, progress payment, or retention release — and the invoice follows the classification. Boring, and bulletproof.
The advance is a tax point
The most expensive assumption in contracting VAT is that tax follows the certificate. It does not. VAT is generally due at the earlier of supply, invoice or payment — and an advance payment is a payment.
Receive a SAR 2 million mobilisation advance and VAT is generally due on it in that period, even though no work has been certified and no progress invoice exists. If the advance sat in the bank for a month before anyone told the accountant, the return for that period is already understated.
The mechanical fix is simple: raise a tax invoice for the advance when it is received, and account for the VAT then.
Recovery has to unwind cleanly
Advances are recovered against later certificates, usually as a percentage deduction. That recovery must reduce the VAT you already accounted for — otherwise you pay twice on the same value.
This is where it goes wrong in practice. The advance invoice is raised by one person, the progress invoices by another, and the recovery is treated as a discount rather than an offset against the advance. The result is VAT accounted for on the advance and again on the gross certificate.
Track the advance as its own balance with its own recovery schedule. When it reaches zero, the VAT should have unwound to zero as well.
Retention is the mirror image
Retention is deducted from a certificate you have already earned. The work is done, the value is certified, and the client holds back five or ten per cent.
The supply has happened. VAT is generally due on the full certified value, not the net amount you were paid. So you remit VAT on money you have not received, and you wait — sometimes a year past handover — for the retention to be released.
This is a real, permanent cash cost of contracting, and it needs to be in the forecast rather than discovered each quarter.
What this means for cash
Put the two together and a contractor can be remitting VAT on advances not yet earned and on retention not yet received, in the same period. Both are correct. Both consume cash.
Which is why the VAT line in a contracting cash forecast should be built from certified value and advances received — not estimated as a percentage of expected collections.
Getting the paperwork right
Three documents keep this clean. A tax invoice for the advance when received. Progress invoices showing gross certified value, the retention deduction and the advance recovery as separate lines. A retention invoice or release document when it is finally paid.
If your progress invoices net everything into one figure, neither you nor an auditor can reconstruct what VAT was due when — and that reconstruction is exactly what gets requested on review.
Key points
- VAT is due at the earlier of supply, invoice or payment
- An advance is a payment, so it triggers VAT before any work is certified
- Advance recovery must offset the VAT already accounted for
- Retention is VAT-able on full certified value, not the net received
- You can be remitting VAT on both unearned and unreceived money at once
Practical checklist
- Raise a tax invoice when an advance is received
- Track each advance with its own recovery schedule
- Show retention and advance recovery as separate invoice lines
- Account for VAT on gross certified value
- Build the VAT forecast from certified value, not collections
- Issue a retention invoice when the balance is released
