A bid increment is the minimum amount by which any new bid must exceed the current highest bid at a public auction. Rather than allowing bidders to raise by arbitrarily small sums — a practice that would stall proceedings and frustrate both buyers and sellers — auction houses publish a tiered schedule of increments, commonly called a bid ladder, that scales upward in proportion to the lot's current price. The system is fundamental to the orderly conduct of fine jewellery and gemstone sales at every major international house, from Sotheby's and Christie's to Bonhams and Philips, and its mechanics directly affect bidding strategy, hammer price outcomes, and the pace of the sale room.

How Increments Are Structured

Increment schedules are almost universally tiered by price band. A representative schedule at a major London or Geneva jewellery sale might operate broadly as follows:

• Below £1,000 (or equivalent currency): increments of £50–£100
• £1,000 to £5,000: increments of £200–£500
• £5,000 to £20,000: increments of £500–£1,000
• £20,000 to £100,000: increments of £2,000–£5,000
• Above £100,000: increments at the auctioneer's discretion, commonly £5,000, £10,000, or larger round figures

Each house publishes its own schedule in its conditions of sale, which form part of the legally binding contract between the house, the consignor, and the buyer. Bidders are expected to have reviewed these terms before participating, whether in the room, by telephone, or via an absentee (commission) bid submitted in advance. The precise thresholds and step sizes vary between houses and may differ between departments within the same house — a specialist jewellery sale may use finer increments at lower bands than a general decorative-arts auction.

The Auctioneer's Discretion

Although the published schedule sets the baseline, auctioneers retain considerable discretion in practice. An experienced auctioneer may accept a bid that falls between standard increments — for instance, taking a bid of £38,000 when the schedule would ordinarily call for £40,000 — if doing so keeps a genuine bidder in the contest and serves the consignor's interest. Conversely, an auctioneer may decline a non-conforming bid that appears intended to disrupt the rhythm of the sale. This latitude is typically reserved for the room; telephone and online bidding platforms generally enforce the published ladder algorithmically, with no human override.

At the very top of the market, where individual lots may carry estimates of several million pounds, the increment itself becomes a material sum. A single step of £100,000 on a Kashmir sapphire or a Golconda diamond is not a trivial formality; it represents a substantive financial commitment, and the auctioneer's judgment about when to call the next increment — and whether to pause for telephone lines — can meaningfully influence the final hammer price.

Absentee and Online Bidding

When a bidder submits a commission (absentee) bid, the auction house's clerk or automated system executes bids on the bidder's behalf up to the stated maximum, advancing by the minimum increment at each step. This means a commission bid of, say, £15,000 will not automatically result in a hammer at £15,000 if competition ceases at £12,000; the system will have bid only as far as necessary to lead the field, typically one increment above the last competing bid. Understanding this mechanism is essential for any serious buyer: the increment schedule determines the granularity with which a commission bid can be optimised.

Online bidding platforms — now standard at virtually all major houses — enforce the published ladder with precision. Some platforms allow a bidder to set a maximum and then compete automatically in real time, mirroring the commission-bid logic. Others require the bidder to click through each increment manually. In either case, the system will reject any attempt to bid below the required minimum advance.

Strategic Implications for Gem and Jewellery Buyers

For buyers of fine gemstones and jewellery, the increment schedule has several practical consequences worth understanding before bidding.

• Psychological thresholds: Bidding tends to cluster at round numbers. A lot trading at £9,500 with a £500 increment will next be called at £10,000 — a psychologically significant barrier that may deter some bidders. Experienced buyers are aware that competition sometimes softens at these transitions.
• Commission bid placement: Setting a commission bid at a figure one increment above a round number (e.g., £10,500 rather than £10,000) can be decisive if a competing bidder has set their maximum at the round figure, since the system will advance past it by exactly one step.
• Telephone bidding: Telephone bidders must respond within seconds; knowing the increment schedule in advance prevents hesitation at critical moments.
• Buyer's premium interaction: The increment affects only the hammer price, not the buyer's premium, which is calculated as a percentage of the hammer. However, a single increment can push a hammer price across a premium band threshold, altering the effective total cost of acquisition.

Publication and Transparency

Reputable auction houses publish their increment schedules in the printed catalogue, on their websites, and in the conditions of sale distributed at registration. This transparency is both a professional standard and, in many jurisdictions, a legal requirement under consumer-protection and distance-selling regulations. Bidders participating online from outside the sale room are entitled to the same information as those present in person. Any material change to the schedule mid-sale would be highly irregular and, in most markets, legally problematic.

For the specialist buyer of coloured gemstones — where a single lot might move from estimate to hammer across a range of several increments in rapid succession — familiarity with the bid ladder is as important as knowledge of the stone itself. The increment is the unit of competition; understanding it is the first discipline of effective auction participation.

Further Reading

• GIA — Buying Gemstones at Auction (Gems & Gemology)