What is an IPC? Interim payment certificates for people who have to live with them
Contractors are not paid when work is done — they are paid when work is certified. The IPC is the document that moves the money, and it deserves to be understood precisely.
On any construction contract of size, the contractor is paid in instalments against progress, and each instalment is authorised by an interim certificate — commonly called an IPC, an interim payment certificate, or a running bill. It is the mechanism that keeps a contractor liquid across a two-year project, and it is where most commercial disputes on a project first become visible.
The cycle, end to end
- 1The contractor submits an application: measured work done to date, priced at BOQ rates, plus materials on site, less everything previously certified.
- 2The engineer or architect (the certifier under most FIDIC-style contracts) checks the measurement against the site and the bill.
- 3A certificate is issued for the approved amount — often less than applied for, and the difference is where arguments live.
- 4Retention is deducted, typically 5–10%, held against defects and released at completion and after the defects period — see retention.
- 5The employer pays against the certificate within the contractual period.
Why IPCs go wrong
Almost every IPC dispute is a measurement dispute wearing commercial clothes. The application says the third floor slab is 100% done; the certifier's records say the pour finished after the cut-off date. The application claims material on site; nobody reconciled the store. The rates disagree because a variation was priced but never formally instructed. None of these are payment problems — they are record problems that surface at payment time.
The paper trail an IPC needs
| Claim in the application | Evidence that settles it |
|---|---|
| Work done to date | Daily site reports with dated photos, progress against BOQ lines |
| Materials on site | Store records: stock in from purchase orders, stock out to works |
| Variations | Written instructions with agreed rates, before execution |
| Previously certified | The certificate history itself — one numbered chain, no gaps |
This is why progress billing sits at the end of a chain rather than being a document you write monthly from scratch. In Ofivio Build, the daily site reports, the BOQ drawdown and the store movements are already one project record — the application's evidence exists because the project was run in it, not because someone assembled a claim file the night before.
See how Build keeps site, store and BOQ as one record — the chain a certificate stands on.
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