The interim payment certificate is the number that pays
A JBCC valuation is the quantity surveyor working out what the work is worth. The interim payment certificate is the principal agent turning that figure into money the employer has to release. Keep the two ideas apart.
QScope Team · 3 February 2026 · 6 min read
On a JBCC building contract the money moves on a document, the interim payment certificate. The contractor does not get paid because the work has value. The contractor gets paid because the principal agent has certified a sum and the clock to payment has started to run.
Who does what
The chain has three roles and it is worth being precise about each one.
- The contractor submits its claim for the work done to the valuation date, usually measured cumulatively against the priced document.
- The quantity surveyor values the work, the materials on site, the variations agreed to date and the retention, and hands the principal agent a recommended figure.
- The principal agent issues the interim payment certificate. That certificate states the amount due, and it is the certificate, not the contractor claim, that the employer pays against.
What the certificate actually contains
A clean interim certificate is cumulative. It states the gross value of everything certified to date, deducts the total previously certified, and the difference is the net amount now due. Retention comes off the gross, VAT at 15 per cent goes on the net, and the recovery statement mechanism sits alongside to deal with amounts the employer is entitled to set against the contractor.
Because the figures are cumulative, an error in one month is not fatal. The next certificate restates the gross position, so an over-certification in month three is pulled back by a lower gross figure in month four. That is the same on-account logic that runs through every progress payment.
Why the certificate, not the claim
The contractor can apply for any figure it likes. The application is a request, not an entitlement. What crystallises the debt is the principal agent putting a number on a certificate, because that is the act the contract ties the payment period to.
This is where contractors lose money without realising it. They chase the value of their application when the number that decides their cash is the one the principal agent certified. If the certificate is low, the place to fix it is the valuation behind it, and the next cycle, not an argument about what should have been claimed.
The discipline
Diary the valuation date the moment the contract is signed and hold to it every month. Reconcile the certificate against your own valuation the day it arrives, so a shortfall is visible while there is still time to raise it. A certificate you did not check is a shortfall you agreed to by silence.
QScope builds the interim valuation line by line and carries the gross, previously certified and net figures straight onto the payment certificate the principal agent signs.