Understanding Auction Estimates

Every lot carries an estimate, expressed as a range: £4,000–6,000, for instance. It is among the most misread figures in the catalogue, and it is worth being precise about what it is.

A considered opinion, not a guarantee

An estimate is the specialist's opinion of the range within which the hammer price is most likely to fall. It is an opinion honestly held and carefully formed, and it is not a promise. Lots sell above estimate and below it, and both outcomes are ordinary.

It is expressed as a range because the market is not a mechanism that returns a single correct number. Two comparable copies of the same book, offered a month apart, may differ in outcome because of condition, provenance, timing, or simply which two collectors happened to be attending.

What the figure is based on

An estimate rests on evidence. In our fields, a specialist normally weighs:

• Auction records for the same or closely comparable material, with attention to condition and completeness rather than headline prices alone.
• Condition, which in paper-based collecting is not a footnote but a principal determinant of value. A repaired tear, a washed sheet, a supplied leaf or a rebacked binding each affect the figure.
• Completeness and issue, particularly for books: the correct plates, maps and advertisements, the right issue points, the presence or absence of a half-title.
• Provenance, where it can be documented. A distinguished former owner or an unbroken chain of ownership adds value; a gap raises questions.
• Rarity in commerce, which is not the same as rarity in institutions. What matters is how often a comparable copy is actually available to buy.
• Present demand, which changes, and which a specialist observes rather than predicts.

Estimates exclude the premium

The estimate refers to the hammer price. Buyer's premium, tax and shipping are additional. A lot estimated at £4,000–6,000 will cost meaningfully more than £6,000 if it sells at the upper figure.

An estimate is not a reserve

The reserve is the confidential minimum below which a lot may not be sold. It is agreed with the consignor, never published, and never set above the low estimate. Where a reserve exists, it is at or below the bottom of the estimate range, so a bid at the low estimate will normally secure the lot.

An estimate is not a formal valuation

A formal valuation is a separate document prepared for a defined purpose — insurance, probate, division of an estate, a charitable transfer — and often to a different basis of value. An insurance valuation reflects the cost of replacement and is typically higher than an auction estimate. A probate valuation reflects open-market value at a fixed date. Do not use an auction estimate for a purpose it was not written for; see [how to request a valuation](/guides/how-to-request-a-valuation).

Why estimates are sometimes conservative

An estimate set at a realistic level attracts bidding, and competition, not the estimate, determines the final price. An estimate set optimistically deters interest and often produces an unsold lot, which is the worst outcome for a consignor. Where you see a figure that seems modest for a distinguished object, it is usually deliberate.

When we decline to estimate

Occasionally an independent specialist may be consulted and will then decline to publish an estimate, or will offer a wide one, because the evidence is genuinely thin: an object of a kind rarely traded, or one whose attribution remains open. We would rather say so than manufacture a figure. Where that is the case, the catalogue will make the position plain.