How to Review Valuation Assumptions Properly

A valuation can be well reasoned and still be vulnerable if one assumption has moved between the working papers and the final report. A market rent of £185 per sq m becomes £195 per sq m in the income approach. A 5.75% equivalent yield is described as 5.5% in the executive summary. The capital value is correct on page 14 but differs by £50,000 from the figure in the certificate.

Knowing how to review valuation assumptions is therefore not simply a final proofreading exercise. It is a structured test of whether the opinion, evidence, calculations and report wording all support one another. The aim is not to second-guess professional judgement. It is to make sure the judgement is clear, evidenced and consistently carried through before the report leaves your desk.

Start by separating facts, assumptions and opinions

The first task is to identify what each key statement actually is. This sounds elementary, but reports often blend confirmed facts, adopted assumptions and valuation conclusions within the same paragraph.

Lease dates, floor areas, passing rents and break options should be checked against the tenancy documentation and instruction material. They are facts, albeit sometimes facts requiring interpretation. Market rent, void period, incentives, yield selection and purchaser costs are assumptions or valuation inputs. Market value and market rent are conclusions.

That distinction matters when reviewing the report. A discrepancy in a stated lease expiry date may change the unexpired term and therefore the yield adopted. A difference in assumed marketing period may affect the treatment of a vacant unit. A conclusion may be entirely reasonable, but it needs to flow from inputs that are stated accurately and consistently.

Start with the basis of value, valuation date, purpose and assumptions. Check these against the instruction before assessing the numbers. A well-supported comparable analysis cannot cure a report that uses the wrong valuation date or has not addressed a special assumption required by the client.

How to review valuation assumptions against the evidence

The central question is straightforward: does the evidence support the assumption, and does the report explain the bridge between the two? The answer will rarely be a mechanical one. Comparable transactions are not identical, and a valuer is expected to exercise judgement. The review should test whether that judgement is visible and proportionate.

Comparable evidence and adjustment

Read each comparable as both a standalone entry and part of the wider set. Check the address, transaction date, tenure, area, price, rent and stated analysis. Then test whether the report uses the same units throughout. A sale analysed at £3,250 per sq m in the comparable schedule should not reappear as £3,520 per sq m in the valuation rationale unless there is a clear reason.

Focus on adjustments where they are material. If a comparable is superior due to location, covenant, condition or lease length, the report should explain how that difference is reflected in the adopted rate or yield. There is no requirement for spurious precision. But a statement that evidence has been adjusted should be more than a label.

The same applies to evidence outside the immediate locality. A transaction from another town, or one completed twelve months before the valuation date, may still be useful. Its weight should be apparent. If it is relied on heavily, the report should show why it remains relevant in the market at the valuation date.

Market rent, incentives and voids

For income-producing property, trace the market rent from the comparable evidence into the cash flow or term and reversion calculation. Check the area basis first. A net internal area in the rental analysis and a gross internal area in the valuation calculation can create a plausible-looking but incorrect figure.

Then review the treatment of incentives, rent-free periods, voids and reletting costs. If recent lettings indicate six months' rent free, but the adopted market rent is described as headline rent with no incentive allowance in the calculation, the report should make the treatment explicit. It may be appropriate to reflect the incentive in the yield, the rent, or a separate cash flow deduction. What matters is that it is not reflected twice, or missed altogether.

Vacant space requires the same discipline. Where the report adopts a three-month marketing period, check that this is consistent with the instruction and with the market commentary. If the calculation assumes nine months to let, the narrative should not state three months without explanation.

Yield selection and lease terms

Yield selection is often where the report's reasoning is most compressed. Review the relationship between the adopted yield, covenant, unexpired term, rent review pattern, void risk and comparable investment evidence. A 5.25% yield may be entirely defensible. It becomes harder to defend if the report also describes short unexpired income, a weak tenant covenant and significant reletting risk without explaining the pricing impact.

Check lease terms carefully. A break option, tenant-only renewal right or unusual review clause can materially affect the income profile. The unexpired term stated in the report should reconcile with the lease dates and valuation date. If the report says 4.2 years unexpired but the dates indicate 3.7 years, it is not a minor presentation point. It may affect the yield rationale and any reversionary analysis.

Read the report as one document

A reliable review does not stop at individual sections. Many issues arise because a report has been prepared in stages, with an amended assumption reflected in one place but not another.

Take the key inputs and follow them across the report: valuation date, market value, market rent, floor area, passing rent, yield, lease expiry, marketing period and capital value. Compare the executive summary, property description, tenancy schedule, comparable analysis, valuation rationale, calculations, certificate and any lender-specific sections.

For example, a report may correctly calculate a market value of £2,450,000 but refer to £2,500,000 in the summary. Alternatively, the stated floor area may be 1,240 sq m in the description but 1,204 sq m in the comparable analysis. These are the sort of inconsistencies that can prompt a query from a reviewer even where the underlying opinion is sound.

Narrative contradictions deserve equal attention. A report cannot comfortably state that demand is limited and supply is elevated, then adopt a short marketing period without setting out the rationale. Nor should it describe a property as fully let if the tenancy schedule identifies a vacant suite. The wording does not need to be uniform, but the underlying story must hold together.

Test the calculation, not just the result

A final value that looks reasonable can conceal an input error. Reperform the critical arithmetic or use an independent check. In an investment valuation, this means checking years purchase, term and reversion inputs, rent commencement dates, purchaser costs and rounding. In a comparable approach, it means checking price per sq m, price per sq ft where used, and the reconciliation from analysed evidence to adopted figure.

Pay close attention to units. A misplaced decimal in an area, an annual rent entered as a monthly amount, or a yield expressed as 0.575 rather than 5.75% can produce obvious errors. More difficult are errors that remain commercially plausible, such as applying a market rent to the wrong area or using the previous draft's yield after the valuation date has changed.

Where a calculation model has been updated, compare the final output with the reported figure rather than assuming the two remain linked. A £50,000 mismatch can be introduced by a late amendment to either document.

Check the instruction and reporting requirements

The report should meet the instruction as well as the valuer's own methodology. Before sign-off, return to the client requirements and make a short list of items that require an explicit response. These may include a stated marketing period, minimum comparable evidence, environmental disclosures, EWS1 information or a required sensitivity commentary.

The review should also confirm that the report addresses the applicable Red Book requirements in the context of the instruction. This is not a box-ticking substitute for professional judgement. It is a way of ensuring that disclosures, assumptions, departures where relevant, valuation uncertainty and reporting statements have not been lost during drafting.

A useful test is to ask whether an informed reader, who has not seen the file, could understand the material assumptions and follow the path to the conclusion. If the answer depends on knowledge held only by the valuer, the report may need a clearer explanation.

Build a review process that works under pressure

The most effective review order follows risk, not page order. First check the instruction, basis, valuation date and headline figures. Then trace the main assumptions through evidence and calculations. Finally, read the report from start to finish for contradictions, omissions and wording that does not reflect the final position.

This can be supported by a second pair of eyes, whether from a colleague or a purpose-built report audit. WriteUp, for example, reads the report across sections and can flag figures that do not reconcile, conflicting lease details, missing required disclosures and inconsistencies in comparable evidence. The surveyor reviews every finding and decides whether it affects the report.

Where software is used, the practical questions are confidentiality and control. Report data should be processed privately and securely, without being retained or used to train models. The tool should support the review, not make the valuation decision.

A careful review will not remove the need for judgement. It gives that judgement a clearer record: the assumptions are stated, the evidence is weighed, the calculations reconcile and the report says what the valuer means. That is what helps a report stand up under scrutiny.