An Interim Payment Certificate (IPC) is a formal document issued by the supervising engineer or project manager certifying the net amount due to the contractor for work executed during a specific billing period, after deducting retention, advance payment recoveries, and previous payments.

In the United States, AIA Document G702 (Application and Certificate for Payment) and G703 (Continuation Sheet / Schedule of Values) are standard administrative forms published by the American Institute of Architects for contractors to submit progress billings.

Under FIDIC Sub-Clause 14.2, an advance mobilization payment is amortized through percentage deductions (typically 10% to 20%) applied to the gross value of each certified IPC once cumulative progress reaches a contractually specified threshold.

Contracts often allow contractors to bill for un-fixed materials delivered to the jobsite (with proof of ownership and insurance) to assist contractor cashflow for long-lead structural items like rebar, structural steel, or mechanical plant.

Under FIDIC Red Book Sub-Clause 14.7, the employer must pay the certified IPC amount within 56 days after the engineer receives the contractor's statement and supporting documents, unless otherwise agreed.

A Schedule of Values is a detailed cost breakdown of the total contract price allocated across specific trade work items, serving as the baseline for evaluating percentage completion on monthly payment applications.

Retention is deducted directly from the gross value of certified work on each progress payment application until the cumulative retention cap is reached, reducing the immediate net payment to the contractor.

If the engineer or architect reduces the requested amount, the contractor can submit additional documentation or dispute the deduction. FIDIC Sub-Clause 14.6 allows the engineer to correct any previous certificate in subsequent IPCs.