A retention cap needs the correct contract value underneath it

The percentage is only half the calculation

Your retention spreadsheet uses a percentage cap, but the builder calculates that cap from a different contract value. Before debating the total held, identify the base each calculation uses. A correct percentage applied to the wrong amount can produce a misleading result, even when both spreadsheets perform their arithmetic perfectly.

Find the actual cap wording

Locate the relevant contract clause and any agreed amendments. Ask the adviser what the wording means for this project, including how variations or adjustments are treated. Do not assume another job's cap applies. This article does not state a universal retention percentage or decide whether a particular amount may lawfully be withheld.

Trace the changes to the contract sum

Business.gov.au's contract guidance recommends documenting agreed changes to a contract. Assemble the original price and the relevant variation records before rebuilding the calculation. Distinguish approved changes, disputed claims and provisional amounts. A running project estimate can include figures that have not been accepted as a change to the contractual basis.

Source: business.gov.au: Prepare a contract

Compare two transparent workings

Imagine your spreadsheet uses the original price while the builder includes a later approved variation. Show the price components, the stated rate and the result in each working. Ask which treatment is supported by the actual terms. The comparison should expose the disputed assumption rather than conceal it inside one unexplained retention total.

Separate cap questions from release questions

Once the calculation is understood, review actual deductions and payments separately. Establishing the cap does not establish the release date, prove every deduction correct or resolve a defect allegation. Keep those questions distinct in the file so an adviser can identify whether the problem concerns calculation, account history, release conditions or more than one issue.

Record the agreed calculation basis

Retain the relevant clause, price schedule and reviewed working with the retention register. If the base remains disputed, label that uncertainty rather than presenting your preferred amount as settled. The next conversation can then address the precise inclusion or exclusion causing the difference, with a reproducible calculation instead of two conflicting percentages applied to unexplained totals.