Rebase only the cost portion tied to a supplied index.
Why can applying an index ratio to the full estimate overstate an adjustment?
Use the matching calculator
Use this decision sequence
- Identify the explicitly indexed share of the original estimate.
- Use original and new values from the same verified index series.
- Leave the unindexed portion on its original basis.
- Compare the arithmetic result with a current complete supplier quote.
Keep the quantities distinct
| Quantity or assumption | How to use it |
|---|---|
| Indexed portion | Changes with the entered ratio. |
| Unindexed portion | Remains at its original nominal value. |
| Actual market quote | Can differ for reasons not captured by that ratio. |
Worked comparison
For a 1,000 USD original estimate with a 60% indexed share, indices of 100 and 120 rebase 600 USD to 720 USD. The unchanged 400 USD portion gives a 1,120 USD total. Applying the 1.2 ratio to all 1,000 USD would instead give 1,200 USD and incorrectly rebase the unindexed share.
Check before using the estimate
No index series, future value or contractual entitlement is selected. The result is not a market forecast. The example values are illustrative arithmetic inputs. Replace them with your measured plan, selected product information and actual quote where relevant.
All dimensions, product properties, prices and specifications in this example are illustrative arithmetic inputs. Use the values from your measured plan, selected product data sheet and supplier quote. This guide does not choose construction specifications or certify safety.
Calculation and scope checked 2026-10-04. Methods and scope.
Related decisions
A small requirement change can add an entire purchase pack
Why is a cost range wider than a proportional quantity range?
Price whole purchase packs
Why does multiplying exact need by a unit price understate a store purchase?
Compare complete supplier baskets
Why can the cheapest quote on each item fail to give the cheapest delivered basket?