HOAI, the German fee scale for architects and engineers, is still the main orientation framework for planning fees in Germany. To calculate a HOAI fee, you need more than one construction cost figure: Honorarzone, Honorarsatz, Leistungsphasen and contractual scope all interact. This is where practices often leave fee behind, usually because assumptions or additional services are not set out clearly.
What The Fee Is Built From
Since 2021, the HOAI fee tables have served as orientation values, not as a fixed minimum and maximum price regime. In practice, the actual fee is usually based on the fee agreement made in Textform, the German requirement for an agreement recorded in text. If no agreement on fee level exists, the Basishonorarsatz, the base fee rate in the relevant table, may become relevant for basic services. For consumers, an additional notice is required that higher or lower fees than the table values can be agreed. This is a legal classification, not legal advice.
Five elements shape the calculation:
- Leistungsbild means the service profile under the HOAI, such as buildings and interiors, outdoor facilities, civil engineering structures, transport facilities, structural design or technical equipment.
- Anrechenbare Kosten are chargeable costs, the cost portions to which the HOAI fee relates. For object and specialist planning, they are usually derived from cost estimates or cost calculations based on DIN 276, the German standard for construction cost classification.
- Honorarzone means fee zone. It grades the difficulty of the planning task.
- Honorarsatz means fee rate. It determines where the calculation sits between the base fee rate and the upper fee rate.
- Leistungsphasen means service phases. They divide a service profile into sections, from initial project analysis to post-completion support.
Only together do these elements create a traceable fee basis. A number from a table is not yet a fee. It must fit the service profile, the commissioned scope and the agreed remuneration.
Determine Fee Zones Carefully
Honorarzonen, or fee zones, classify planning requirements. For buildings and interiors, they range from zone I for very low requirements to zone V for very high requirements. Other service profiles may use their own criteria and ranges. The key point is that the zone should not be chosen by instinct, but by the assessment criteria for the relevant service profile.
Bewertungsmerkmale are assessment criteria, for example design, structural, technical, functional or coordination requirements. Objektlisten are object lists in the HOAI annexes. They provide rule-of-thumb examples that assign typical objects to fee zones. They do not replace project-specific assessment, but they help explain it.
Typical mistakes arise when a project is placed in a zone too early and that assumption is never revisited. A building that looked ordinary at the start may become more complex because of existing fabric, tight site conditions, fire safety, demanding use or intensive coordination. Conversely, a higher fee zone only stands up if the requirements actually exist and are documented.
In practical terms, record the applicable service profile, the relevant assessment criteria, the object list used and the reason why the selected zone is plausible. This reasoning should align with the contract, the cost calculation and later project changes.
Fee Rate And Section 13 Interpolation
A Honorartafel is a HOAI fee table. It shows the fee range for a service profile, a fee zone and a cost value. The Basishonorarsatz is the lower table value. The oberer Honorarsatz is the upper table value. Between them, the parties can agree a fee rate, for example a mid-range value or a project-specific rate.
Section 13 HOAI governs interpolation. Interpolation means that if the chargeable costs sit between two table values, the intermediate amount is calculated linearly. This is not an estimate. It is a ratio calculation.
Example: A building is assigned to fee zone III. The chargeable costs are EUR 1,780,000. The fee table for buildings and interiors contains values at EUR 1,500,000 and EUR 2,000,000. At the base fee rate, the zone III values are EUR 165,911 and EUR 214,108. EUR 1,780,000 sits 56 per cent between the two cost values. The interpolated base fee rate is therefore around EUR 192,900. For the upper fee rate, interpolation between EUR 206,923 and EUR 267,034 gives around EUR 240,600.
If the parties agree, as an example, a mid-range value within this span, the full basic fee is around EUR 216,800. Basic fee here means the fee for all basic services in the service profile, before VAT, expenses, conversion surcharges and special services. If only service phases 1 to 8 are commissioned for a building, the building service profile applies 98 per cent, which gives around EUR 212,500.
Service Phases Are Fee Shares, Not Hours
Leistungsphasen, often abbreviated as LPH, divide a service profile into remunerated stages. For buildings, the full scope uses these fee shares:
- LPH 1 Initial project analysis: 2 per cent
- LPH 2 Preliminary design: 7 per cent
- LPH 3 Design planning: 15 per cent
- LPH 4 Approval planning: 3 per cent
- LPH 5 Detailed design: 25 per cent
- LPH 6 Preparation of procurement: 10 per cent
- LPH 7 Participation in procurement: 4 per cent
- LPH 8 Site supervision and documentation: 32 per cent
- LPH 9 Post-completion support: 2 per cent
These percentages are fee shares, not time budgets. In buildings, LPH 8 carries the largest share at 32 per cent because site supervision and documentation require ongoing presence, review and coordination. For interiors and other service profiles, individual percentages may differ.
Grundleistungen are basic services that are normally required within a service profile. Besondere Leistungen are special services, additional services that should be agreed separately. If only parts of a service phase are commissioned, usually only the corresponding share should be applied. If more is requested later, a clear follow-up commission is needed.
Where Practices Leave Fee Behind
Many fee losses happen before the calculation itself. Common weak points are:
- The fee agreement remains too general or is not updated cleanly in text form.
- The fee zone is not explained, even though planning requirements increase.
- Chargeable costs are set too low or are not updated after the cost calculation.
- Mitzuverarbeitende Bausubstanz is missed. This means existing building fabric that is technically or creatively incorporated into the planning.
- Conversion or modernisation surcharges are not agreed, although the existing building creates additional work.
- Special services, such as additional options, funding documents, deeper condition surveys or specific documentation, are carried out without a commission, fee basis and evidence.
- Scope changes are solved technically, but are not reassessed under Section 10 HOAI or under the contract.
- LPH 9 is not commissioned, yet post-completion support tasks still enter day-to-day work.
Software cannot replace these decisions. It can make deadlines, project states, evidence and calculation paths visible. Whether an entitlement exists, whether a service has been commissioned and how the contract should be read remains a professional and, where needed, legal assessment.
Conclusion: Calculate Clearly, Agree Clearly
To calculate a HOAI fee properly, treat the calculation as a chain from the beginning: service profile, chargeable costs, fee zone, fee rate, interpolation, service phases and additional services. The main lever is often not a larger number, but a better-documented basis.
Structify helps practices keep cost states, service phases, fee zones, agreements and evidence in one project context. You can find more on the HOAI fee module; for initial orientation, use the HOAI calculator. If you would like to see what this looks like on your project, book a short online demo.