1. Two correct uses
Only two situations in which applying the index is methodologically correct. Both concern change rather than level.
Updating an older estimate, where a fresh calculation is not possible or reasonable.
As the basis of a contractual price adjustment, where the parties have agreed it in advance. The indicator and the base quarter are named in the contract.
All other uses are interpretations, not calculations, and should be presented as such. An interpretation should be stated as such.
2. Four conditions
These must be met before applying the index. Otherwise the result cannot be checked.
| Condition | Why |
|---|---|
| The right building group | cost structure differs by building type |
| The right indicator, new build or repair and reconstruction | these are different indices |
| A clear base date | the index measures change between two points |
| Knowing which cost layer is being updated | the index covers direct costs |
The fourth condition means in practice that multiplying the total price of an old quotation by the index change assumes overheads and profit moved at the same rate. That assumption is rarely true.
3. When the index misleads
Four situations where the result is wrong. They stem from the wrong indicator or the wrong base.
| Situation | Why the result is wrong |
|---|---|
| The project has changed in the meantime | the index updates a price, not a scope |
| The building type does not match the indicator | wrong cost structure |
| The period is long | the cost structure itself may have changed |
| The market has shifted sharply | margin moves independently of inputs |
The first situation is the commonest and the easiest to miss. A two year old estimate almost always concerns a slightly different building, and indexing it then gives a precise figure about the wrong thing.
4. What to specify in a contract
Four points, without which an indexation clause is not workable. They concern the indicator, the base date and the scope.
Which indicator exactly, with the building group and type named.
Which base date or base period.
Which part of the price is indexed, because it is usually not the whole sum. That part is named in the contract.
At what frequency, and with what publication lag.
The fourth point matters in the Estonian context, because the index is published quarterly and after the quarter has ended. This means that at the moment a contract is signed the current quarter's figure is not yet known, and the indexation clause must say what is used in that case.
5. The simplest correct use
One approach works almost always: use the index for direction, not for an exact sum. The result then stays defensible.
| Say | Do not say |
|---|---|
| Input costs have risen by roughly this much over the period, so the old estimate is probably low | The old estimate multiplied by the index gives the new price |
The first statement is true and useful. The second is apparently precise and substantively wrong: it produces a sum calculated to the cent on a basis that does not hold.
In summary, and four practical rules
The methodologically correct use of the index is limited to two situations: updating an older estimate and contractual price adjustment. Four conditions must be met before applying it, and four situations make the result wrong, of which the commonest is that the project itself has changed. A contract must specify the indicator, the base date, the indexed portion and the publication lag, because the index is published quarterly after the quarter has ended.
Four rules: check whether the project has changed before any indexation. Name the indicator used precisely, especially in a contractual context. Allow for the publication lag, because the current quarter's data do not yet exist. Present the result as a direction where the use is not contractual.
This article serves professional orientation at the date of checking. It is not a quotation.