What to take into your next appraisal
- Record evidence dates, units and unresolved scope as well as values.
- Keep scenario overrides separate from the approved base case.
- Use review triggers tied to project events, not just calendar reminders.
Give each material assumption a stable identity
Use a stable ID for each assumption and record its value, unit, source, source date, owner, evidence status and next review trigger. Separate the source's observation date from the date the modeller downloaded it. A current download of a two-year-old valuation does not create a current valuation.
The CSV includes a completed fictional base case and two scenario changes. Copy the structure, replace every example with project evidence, and store documents in an accessible project record. Do not invent evidence references to make an incomplete model appear reviewed.
Sources: UK Government: The AQuA Book; ICAEW: 20 principles for good spreadsheet practice, 2024 edition
Follow a price input into the model
Assumption R01 is a fictional price of 200,000 currency units per apartment, taken from a fictional quotation dated 1 September. With 100 units, base gross revenue is 20m. A controlled 5% reduction changes price to 190,000 and revenue to 19m. The 1m bridge should match the revenue schedule exactly.
If the model uses price per square metre, the register must identify the area definition too. A per-unit quote cannot be copied into an area-rate cell without conversion and a clear unit mix. Keep parking, incentives and recoverable taxes separate where their treatment differs.
| ID | Base | Downside | Evidence status |
|---|---|---|---|
| R01 price per unit | 200,000 | 190,000 | Fictional quote; downside is a sensitivity |
| T01 settlement month | 24 | 30 | Fictional programme; delay is a sensitivity |
Preserve a change history instead of overwriting
Record the old value, new value, effective scenario, reason, author and approval state. The example keeps R01 at 200,000 in Base v1 and adds 190,000 in Downside v2. Updating a sensitivity must not overwrite the supporting source or approved base.
When a real tender replaces a provisional budget, retain both records and explain the scope change. A lower tender price with exclusions is not necessarily a like-for-like saving. Link each run to the precise input set and keep the resulting outputs with it.
Make uncertainty visible to the decision maker
Flag inputs as observed, quoted, agreed, assumed or unresolved. These labels describe evidence status; they are not numerical probabilities. Set a review trigger such as a tender return, planning decision, lender term sheet or material market movement.
Prioritise stale assumptions by decision sensitivity. An old low-value administrative allowance may matter less than an unconfirmed completion date that shifts sales and loan maturity. An owner should either replace weak evidence, widen the tested range or state why the decision can tolerate it.
Connect the register to review and handover
Before issue, trace headline outputs back to input IDs and sample the supporting records. Check that the published scenario matches the committee paper and that no unresolved placeholder appears as a firm commitment. Keep confidential quotations in controlled project storage rather than public article downloads.
The register does not replace commercial judgement or specialist review. Its value is making the evidence and uncertainty inspectable by the next reviewer, even when the original modeller is unavailable.
Sources: UK Government: The AQuA Book; ICAEW: 20 principles for good spreadsheet practice, 2024 edition
Sources and further reading
- The AQuA Book UK Government
- 20 principles for good spreadsheet practice, 2024 edition ICAEW
Published by Feasly. How we prepare our guides. Suggest a correction.
