The four conditions of a comparable estimate
An estimate works as a control tool only if it states its own basis. The client need not redo the sums, only check that the estimate says where the figures come from and that this basis matches the previous estimate and the budget.
| Condition | Question to put to the designer | Warning sign |
|---|---|---|
| Same quantities | Are the quantities measured on this stage's drawings or carried over from the previous stage? | Quantities unchanged from one stage to the next while the design has changed |
| Same price date | Which month and year do the unit prices refer to? | No date, or a date different from the budget's with no stated update |
| Same items | Which works are included, which excluded, which deferred to later choices? | Items that disappear without explanation, "extra" or "to be defined" with no figure |
| Same price list | Which prezzario (official price list) or which price analyses were used? | A change of price list between two stages, lump-sum prices with no breakdown |
VAT must be handled separately, and always in the same way. The simplest rule is to write the budget and request every estimate net of IVA (Italian VAT), with the tax on a separate line of the total cost.
In the public sector, the estimate is a mandatory document
The public contracts code sets out the estimating documents for each design level. The progetto di fattibilità tecnico economica (technical and economic feasibility design) includes the "estimate of the works" and the "economic summary of the project" (Annex I.7 to Legislative Decree 36/2023, art. 6(7)(i) and (l), unofficial translation). The progetto esecutivo (detailed design) includes, "unless the contracting authority determines otherwise with reasons", the programme, the list of unit prices with the related analyses, the computo metrico estimativo (priced bill of quantities) and the quadro economico (economic summary), the draft contract and the special specification (art. 22(4)).
The public design then goes through verification and validation. The stazione appaltante (contracting authority) verifies that the design complies with the documento di indirizzo alla progettazione (design brief) and with the rules while the design is being developed (Legislative Decree 36/2023, art. 42(1)); validation, signed by the RUP (the single project manager), is the formal act that takes up the results (para. 4). Since the design brief states "the economic limits to be respected" (Annex I.7, art. 3(g)), checking the estimate on public works is first and foremost a check of consistency with those limits.
In the private sector, the documents are requested by contract
No rule requires the designer of a private project to produce an estimate at every stage. A client who wants a priced bill at every design level must write it into the appointment: which estimate, at which stage, in what detail, on which price list, at which date. The priced bill of quantities, how it is prepared and the price lists are covered in the dedicated guide to the bill of quantities. The public model is a good template for the private sector too: an estimate at feasibility stage, a priced estimate on the design submitted for the building permit, and a priced bill of quantities with a price schedule on the detailed design give three control points before the works are awarded.
Three readings at every stage
At each submission, the estimate is read against three references. The first reading is against the budget: net of VAT and at the same price date, does the estimate sit within the spending limit for the works? If it exceeds it, by how much and on which items?
The second is against the previous estimate: every increase should be explained by updated prices, better measured quantities or a changed brief. A gap that fits none of the three causes is a problem of method. The third is against an independent estimate, when the amount or the risk justifies it.
A gap found at design stage costs a revision; the same gap found when the tenders are opened costs a whole procedure. That is why checking the estimate is the most profitable moment for the budget.
The articles in this branch
- The article Design over budget: what the client can do starts from the absence, in the sources examined, of a tolerance threshold and sets out what strengthens or weakens the client's position.
- The article The estimate exceeds the budget: what to do before awarding the works offers a three-cause diagnosis and the order in which to use the levers to get back within budget.
- The article Preparing the budget recovery note when the estimate exceeds the budget describes the 2-page document that turns the gap into a signed decision, with a fictitious example.
- The article The independent cost check explains when to commission one, from whom, on which documents and within what limits.
- The article Design verification and validation: what they check on cost covers the check the public contracts code requires of the contracting authority before the tender.
This article sets out the state of the rules as at 21 October 2026 and is intended for guidance. It does not replace legal advice or an examination of the specific case.