Fees as Percentages: Line Items Calculated from a Base Value
What this is about
Many professional fee scales don't work with unit prices but with shares of a total value: the German HOAI splits an architect's fee into service phases (phase 5 = 25 %, phase 8 = 32 % …), the Swiss SIA regulations use partial services in percent, and project management per AHO follows the same pattern.
That's exactly what the dynamic item “Share of Base Value” is for: store the total once per document and enter just the percentage per line – GrandTotal does the math.
How it works
Insert a dynamic item and pick “Share of Base Value”. If the document has no base value yet, GrandTotal asks for it right away – once per invoice or estimate. From then on the percentage is simply the item's quantity:
The unit price shows the value of one percent – so each line reads like a verifiable calculation: 25 % × 1,000.00 = 25,000.00.
The base value
The base value lives in the document info and applies to all percentage items of the invoice. When it changes – say, an updated cost calculation – every item recalculates instantly. The field even accepts formulas: 350000*1.19 is evaluated as you leave the field.
The base value field only appears once the document contains at least one “Share of Base Value” item.
Interactive templates for HOAI and SIA 102
For the two most common fee scales there are ready-made interactive document templates: install the HOAI or SIA 102 plugin via Overview → Get Plugins and the template appears under File → New → Invoice.
A form asks for the key figures – chargeable costs, fee zone and rate per HOAI, or building category and hourly rate per SIA 102, plus the completion per service phase. The result is a finished draft invoice: the derivation goes into the introduction, the total fee becomes the base value, each phase a percentage item. The HOAI template can even determine the fee zone from the evaluation criteria per § 35.
Not just for architects
The “total × rate” pattern appears in many fee scales: SIA 102/103/108 in Switzerland, AHO project management, the tenth-rates of German tax consultants or lawyer fees per RVG. Percentage items work in estimates too; converting to an invoice carries the base value along.
At a Glance
Percentage = quantity
Enter just the rate per item – GrandTotal calculates the amount.
One base value per document
Stored in the document info, requested when you pick the item type.
Live recalculation
Change the base value – all percentage items update instantly.
Formulas in the field
Entries like 350000*1.19 are calculated on the spot.
Estimates too
Converting to an invoice carries the base value along.
Ready-made templates
HOAI and SIA 102 as interactive templates – install via Overview → Get Plugins, use under File → New.