Interim Valuation Calculator

An interim valuation is a periodic assessment of the value of construction work completed to date on a contract, carried out in order to calculate the amount due to the contractor at that point in the project. It is called "interim" because it is not the final settlement — it is a payment on account, with the understanding that all amounts are provisional until the final account is agreed and the Final Certificate is issued.

The fundamental reason interim valuations exist is that construction projects take months or years to complete, and no contractor can be expected to finance the entire cost of a project from their own resources and wait until completion for payment. Interim valuations allow the contractor to recover their costs progressively as work is completed, maintaining a manageable cash flow position throughout the project.

In Nigerian construction practice, the valuation process typically works as follows: the contractor submits a detailed payment application to the supervising consultant (Architect or Engineer) and the client's Quantity Surveyor; the QS then measures and values the work, sometimes jointly with the contractor's QS; the supervising consultant issues an Interim Certificate for the agreed amount; and the client makes payment within the contractually specified period. This process repeats monthly (or at the agreed certification interval) throughout the project.

The quality of a contractor's valuation application — how clearly it is organised, how well it is supported by measured drawings, and how closely it reflects the contract requirements — directly affects how quickly the QS can certify and how much is agreed first time. A poorly presented claim causes delays while the QS requests additional information, which delays payment. Nigerian contractors who invest in proper QS support for their valuation applications consistently receive faster payment than those who submit informal or incomplete claims.

Several contract forms are in common use in Nigerian construction, each with slightly different provisions for interim payment. The most important are: the NIQS Standard Conditions of Contract (developed by the Nigerian Institute of Quantity Surveyors and widely used on public sector building work); the JCT Standard Form with Nigerian amendments (particularly on private-sector projects influenced by UK practice); the FIDIC Red Book 1999/2017 (used on civil engineering and donor-funded projects); and increasingly, the NEC4 Engineering and Construction Contract on World Bank-funded infrastructure projects.

Each of these forms has specific payment clause mechanics. FIDIC Clause 14 requires the contractor to submit a monthly Statement; the Engineer certifies within 28 days; the Employer pays within 28 days of certification. NIQS conditions typically require monthly valuations with payment within 14–21 days of certificate issue, though the reality of public sector payment is often significantly slower. JCT-based contracts in Nigeria often follow the UK standard of a 14-day notice period and 5-day final date for payment.

For practical purposes, the key provisions to understand in any Nigerian construction contract are: the due date for making a payment application; how long the QS/Engineer has to certify; how long the client has to pay after certification; what interest accrues on late payment; and what the procedure is for disputed certificates. Getting these dates into a monthly calendar reminder at contract commencement eliminates the most common administrative cause of payment delay — late submission by the contractor.

Preliminaries are the costs of establishing and maintaining the site organisation — everything that is not directly measurable as a work item but is essential to deliver the project. They include site management staff, site offices and welfare facilities, temporary fencing and security, scaffolding, small plant and tools, consumables, insurance premiums, bonds and guarantees, temporary roads and drainage, and the cost of meeting health and safety requirements.

Valuing preliminaries in an interim certificate is more complex than valuing measured work because many preliminary items are time-related (costs that accrue daily or monthly) rather than output-related. The standard approaches are: (1) a percentage of measured work — preliminaries are valued at the same percentage as measured work completion, on the basis that if 40% of measured work is done, 40% of preliminaries have been incurred; (2) a time-related assessment — each preliminary item is assessed separately based on what proportion of its cost has been incurred to date; or (3) a fixed/time split — each item is divided into a fixed element (establishment cost, incurred once at the start) and a time-related element (recurring monthly cost).

On Nigerian public sector contracts, the percentage-of-completion method is most commonly used for simplicity. For larger or more complex projects, a detailed preliminary schedule with monthly costs provides more accurate valuation and reduces disputes. This calculator uses the percentage-of-completion approach, applying the preliminaries percentage to the stated proportion of preliminaries spent.

A variation (or variation order, VO) is an instruction from the client or their representative to change the scope of work originally described in the contract. Variations can add work (additional items), omit work (deductions), or change the character or quality of specified work. On most Nigerian construction contracts, only authorised variations — those instructed in writing by the named representative — are payable. Verbal instructions to change scope, without written confirmation, create significant risk of non-payment.

Variations are valued by: (1) using rates in the priced BOQ for similar work; (2) using pro-rata rates derived from BOQ rates for work of a similar character; (3) daywork (labour, plant, and material costs plus a percentage for overhead and profit) for work that cannot be measured in advance; or (4) by agreement between the parties. In practice, variation valuation is one of the most contentious areas in Nigerian construction contracts, with disputes often arising because the contractor includes costs in variations that the client considers already covered by the contract rates.

Variation instructions should be formally acknowledged by the contractor and, where possible, the value agreed before work proceeds. In Nigeria, where project administration is often informal, contractors frequently carry out varied work on verbal instruction and then attempt to agree the value retrospectively — a practice that regularly leads to underpayment. The professional approach is to issue a written Variation Quotation before proceeding wherever the scope is clear enough to price.

Retention serves as a financial guarantee held by the client that the contractor will return to rectify defects during the Defects Liability Period. The standard Nigerian practice mirrors JCT and FIDIC conventions: a retention percentage (typically 5%) is deducted from each interim certificate, up to a retention limit (typically 5% of the contract sum); half is released at Practical Completion; the remaining half is released at the end of the Defects Liability Period, which is typically 12 months after Practical Completion on building contracts and 24 months on certain civil engineering and infrastructure contracts.

In practice, the release of the second half of retention in Nigeria is the most disputed and delayed element of construction payment. Clients frequently delay issuing the Final Certificate (which triggers second-half retention release) for years after the DLP has expired, either through administrative inaction or deliberate withholding pending final account agreement. Nigerian contractors should pursue Final Certificate issue actively once the DLP ends, and should document all defect rectification work carefully to demonstrate that the DLP obligations have been fulfilled.

The final account is the agreed statement of the total value of the contract, including all variations, fluctuations, loss and expense claims, and any other adjustments. It is the foundation of the Final Certificate. Reaching a final account agreement often requires several rounds of negotiation between the contractor's QS and the client's QS, and in contested cases, may proceed to adjudication or arbitration. Nigerian courts have jurisdiction over construction disputes, but the lengthy court process makes arbitration (under the Arbitration and Conciliation Act 2023) the preferred dispute resolution route for most commercial construction contracts.

For contractors managing their business performance, tracking retention balances across all contracts is an important treasury function. The aggregate of all retention balances due represents real money that the business has earned but not yet collected — for a contractor with ₦1 billion in active and recently completed contracts at 5% retention, this may represent ₦25–50 million in locked-up cash. Prompt pursuit of Practical Completion certificates, early completion of DLP obligations, and active follow-up on Final Certificate issue are commercial disciplines that directly affect cash position.

Late payment is endemic in Nigerian construction, particularly on public sector contracts. Government clients at federal and state level routinely pay 90–360 days beyond the contractual payment date, citing cash flow constraints, budget release delays, and verification requirements. The practical effect is that contractors fund government construction programmes from their own working capital, often at significant financial cost and with no compensation.

The legal position is improving. Under FIDIC contracts, Clause 14.8 provides for financing charges at 3% above the central bank rate on late payments. Under the Nigerian Arbitration and Conciliation Act 2023, arbitrators and courts have clearer powers to award interest and costs on construction disputes. Several recent cases in Nigerian courts have affirmed contractors' rights to interest on overdue certificates.

Practical measures Nigerian contractors use to mitigate late payment risk include: thorough pre-qualification of clients (reviewing payment history before accepting a contract); requiring performance bonds from clients on large contracts; building financing cost provisions into tender prices for contracts with slow-paying clients; maintaining strong banking relationships to ensure overdraft facilities are available when needed; and subcontracting a higher proportion of work to transfer cash flow pressure to subcontractors (while understanding the ethical and legal implications of doing so).