Project records for an engineering firm: how do you keep track of hours, extra work and post-calculation per project?

Good project records at an engineering firm consist of four things: a clear assignment per phase, hours per project and per phase, a recorded agreement for every change, and a post-calculation after each phase. With them you can invoice extra work, support your invoices and make better quotations.

The law and the standard terms DNR2025 give you something to hold on to. They say what you may charge if nothing was agreed, when a change gives a right to extra fees, and what you get if the client stops halfway. In all those cases your time records are the evidence.

In this article

1. What belongs in the records of a single project?
2. Why record every hour on a project, also with a fixed price?
3. When is additional work extra work that you may invoice?
4. How do you record extra work so that you can invoice it?
5. What is post-calculation and what does it teach you?
6. How do you deal with indexation on a project that runs for years?
7. What may you charge if the client stops halfway?
8. How long do you keep the project records?

What belongs in the records of a single project?

For each project you keep the assignment, the hours, the costs, the changes and the invoices, on one project code. If you do that well, you can say at any moment how much of the fee has already been earned and what is still outstanding.

• The assignment: which phases and which tasks, and which not. Also record the form of the fee: time and materials, a fixed amount per phase or a percentage of the construction costs.
• The hours: per employee, per day, per phase, with a short description of the work.
• Additional costs: such as travel, inspections, software, reproductions and fees, if you may charge them separately.
• Changes: who asked for what, when, with what effects, and who agreed.
• Invoices and payments: per instalment, with the phase and hours they belong to.

The examples of additional costs come from DNR2025, the standard terms of BNA and NLingenieurs for architects and engineers. They mention travel and accommodation costs, inspection costs, measuring instruments, software, reproductions, telecommunications, registrations and fees, to the extent the parties agree on them (DNR2025, article 1).

The Belastingdienst also sets requirements. Every business owner must keep records that fit the requirements of the business, so that its rights and obligations are clear from them at any moment. You keep that data for seven years (General Tax Act, article 52). At a consultancy firm the timesheets and the assignment confirmations belong to that as well, because the revenue rests on them.

Why record every hour on a project, also with a fixed price?

Because without hours you do not know whether a fixed price makes or loses money. With a time-and-materials assignment the hours are your invoice. With a fixed price they are your yardstick for progress and profit. And in a dispute or a termination they are your evidence.

DNR2025 says that with a fee based on time the rates per unit of time are agreed in writing. Time spent means the hours for the assignment, plus the travel time needed for it (DNR2025, article 12.1). So record travel time separately, so that you can show it.

The client may check your invoice. DNR2025 says that invoices must be itemised so that they can be checked and traced back to the assignment. If the client disputes an invoice, he can have it checked by an accountant. You give that accountant access to your books (DNR2025, articles 13.3 and 13.8).

If no price was agreed, the law applies. A client who did not agree a fee with you owes the remuneration calculated in the usual way, and otherwise a reasonable remuneration (Civil Code, article 7:405(2)). Then too you must show how much work you did. That is only possible with time records.

When is additional work extra work that you may invoice?

If it falls outside the agreed assignment and the cause lies with the client. If you work with DNR2025, a change gives a right to extra fees and more time if it is needed because of a choice by the client or the client's advisers, because of new laws and regulations, or because of circumstances that are at the client's risk (DNR2025, article 17.4).

If the change is caused by a mistake of your own, it cannot be charged as extra. An exception is work that would have been needed anyway, even without that mistake (DNR2025, article 17.5). If the assignment was delayed or suspended by the client, you are entitled to compensation for the reasonable costs of that (DNR2025, article 17.6).

Whether something falls outside the assignment depends on how precisely the assignment is described. That is what the Standard Task Description STB2026 was made for. With it, client and consultants agree per project and per phase which tasks will be carried out, and therefore also which will not (BNA and NLingenieurs, STB2026 alpha version, 17 June 2026). A task that is not in your assignment is easier to recognise as extra work later.

Changes by the client are not an exception. In a study of two Australian construction projects, rework cost 3.15% and 2.40% of the contract value. The main causes were changes by the client and the end user, and errors and omissions in the contract documents (Love & Li, 2000). It concerned two projects, so it says nothing about an average. It does show where the extra hours come from.

How do you record extra work so that you can invoice it?

In writing and in advance. DNR2025 says that every change to the assignment is agreed between the parties in good time and put in writing. The consultant informs the client in good time of the effects on planning, fees, construction costs and quality (DNR2025, articles 17.1 and 17.3).

In practice, a simple change form or an email with a fixed layout works: date, who asked for the change, what changes, how many hours and what amount, the effect on the planning, and the client's approval. Give the change its own code in your time records. Then at invoicing you can see exactly which hours belong to it.

Do not wait for the final account. The later you report a change, the harder it is to show that the work fell outside the assignment. The same lesson applies in other trades, for example for a painter who only puts extra work on the final invoice (extra work and the quotation for painters).

What is post-calculation and what does it teach you?

Post-calculation means comparing the actual hours and costs of a project with what you budgeted in advance. Do it per phase, not only at the end. Then you see in time where an assignment is overrunning, and you can still talk to the client about extra work or the planning.

In the example a building services consultant budgets 400 hours at € 105, a fixed fee of € 42,000. It became 496 hours. Of those, 25 hours were changes by the client that had been recorded in advance. The firm invoices them as extra work, € 2,625. The income per hour worked then becomes € 89.97. Without recorded extra work it would have been € 84.68.

That estimates turn out too low is no coincidence. In a study of 258 infrastructure projects, the actual construction costs were on average 28% higher than estimated. In almost 9 out of 10 projects the costs were underestimated (Flyvbjerg, Holm & Buhl, 2002). That research was about the construction costs of large projects, not about the hours of a consultancy firm. It does show that an estimate is more often too low than too high.

So use your post-calculations as the basis for the next quotation. Keep track, per type of assignment and per phase, of how many hours it really took. The same idea is worked out for a roofing business in a separate article (pre-calculation and post-calculation).

How do you deal with indexation on a project that runs for years?

Agree an indexation, or let the standard rule of DNR2025 apply. DNR2025 says that the fee is indexed periodically in a way the parties agree. If nothing was agreed, the fee follows the CBS collective wage index for architects' and engineering firms every year on 1 January, measured in October (DNR2025, article 12.2).

For your records that means: keep track per project of which hours fall in which year and at which rate. An assignment accepted in 2025 and still running in 2027 then has two or three rates. Put the rate per period in the assignment, so you do not have to discuss it at invoicing.

What may you charge if the client stops halfway?

A reasonable part of the fee. The law says that you are then entitled to a part of the remuneration to be determined reasonably. This takes into account, among other things, the work you already did, the benefit the client has from it, and the reason why the assignment ended (Civil Code, article 7:411).

DNR2025 works this out. The parties establish the state of the work on the day the notice period ends. The client pays the fee and additional costs up to that moment, plus reasonable costs from commitments you had already made. If the client terminates without grounds, you may charge 10% of the remaining fee as a termination fee, except with a consumer (DNR2025, articles 18.7, 19.1 and 19.4).

Establishing the state of the work only works with good project records. Hours per phase, delivered drawings and calculations, and recorded changes show how far you had got. Without that data it becomes a discussion about an estimate.

How long do you keep the project records?

For tax purposes, seven years. That applies to the books and the documents that belong to them, such as timesheets, assignment confirmations and invoices (General Tax Act, article 52(4)).

There is another reason to keep the project file. Under DNR2025 a business claim against the consultant lapses five years after the assignment ends or is completed (DNR2025, article 14.11). If you are held liable during that period, you want to be able to show what the assignment was, which changes came and who agreed to what.

Sources

• BNA and Royal NLingenieurs, De Nieuwe Regeling 2025 (DNR2025), main document, articles 1, 12, 13, 14.11, 17, 18 and 19 (in Dutch). bna.nl
• General Tax Act (Algemene wet inzake rijksbelastingen), article 52, in force from 1 October 2026. wetten.overheid.nl
• Dutch Civil Code Book 7, articles 405 and 411, in force from 8 October 2026. wetten.overheid.nl
• BNA and NLingenieurs, STB2026 alpha version, explanation and manual, version 1.0, 17 June 2026 (in Dutch). bna.nl
• Love, P.E.D. & Li, H. (2000). Quantifying the causes and costs of rework in construction. Construction Management and Economics, 18(4), 479-490. doi.org
• Flyvbjerg, B., Holm, M.S. & Buhl, S. (2002). Underestimating costs in public works projects: error or lie? Journal of the American Planning Association, 68(3), 279-295. doi.org