How to Build a 12-Month Diamond Stock Plan: Forecasting Demand by Shape, Carat, and Season

A 12-month stock plan connects your sales history to your buying decisions. For lab-grown diamond retailers, it serves a specific function: reducing over-ordering during quiet periods while ensuring adequate inventory depth when demand peaks. Without a forward-looking plan, retailers either absorb excess carrying cost through slow months or lose margin on sales during peak periods because the right stock was not in place.

Step 1: Audit Last Year's Sales by Shape

For each shape in your current range, record units sold by month, average selling price by month, and any months where stock ran out before the period ended. If your range covers round brilliant diamonds, oval cut diamonds, cushion cuts, pear shapes, emerald cuts, and marquise diamonds, this audit will immediately show which shapes drove volume and which absorbed cost without proportionate margin return.

For retailers adding new shapes to their range — such as radiant cuts or asscher cuts — set conservative initial stock levels and review velocity after the first 90-day rotation cycle. The most popular diamond shapes guide covers which shapes European retailers are prioritising in 2026. Contact the LabGems team for guidance on current order patterns.

Step 2: Map Your Seasonal Demand Peaks

Four periods generate reliably elevated demand for European retail jewellers. Build stock for each window approximately 30 to 35 days before the peak begins — this accounts for the approximately 3 to 5 day delivery window from Antwerp plus display preparation time.

• Valentine's season (mid-January to 14 February): Certified loose diamonds in the 0.50ct to 1.00ct range move at elevated velocity. Stock for this window should be in display by approximately 20 January.

• Spring bridal season (late March to early May): Oval cut diamonds, round brilliants, and cushion cuts in the 1.00ct to 2.00ct range see the most sustained uplift of the year. The highest volume peak for bridal-focused retailers.

• Pre-summer gifting (May to June): Lighter designs using melee diamonds and coloured lab-grown diamonds perform well alongside bridal. Include lab-grown gemstones in this window for broader gifting appeal.

• Christmas (late October to 24 December): The broadest peak across all shapes. Build certified diamond stock from the first week of October. The short Antwerp dispatch window gives reorder flexibility through November.

The periods between peaks — mid-February to mid-March, June to August, September, and early January — are your carrying cost risk windows. Stock ordered in excess during these months generates cost without proportionate margin return. This is where the 90-day rotation model provides the tightest discipline.

Step 3: Allocate Inventory by Carat Weight

Carat distribution in your plan should reflect your customer base and price point. A conservative starting allocation by unit count for most mid-market European retailers:

• Approximately 40 percent in the 0.30ct to 0.70ct range: highest turnover, lowest per-unit carrying cost

• Approximately 35 percent in the 0.70ct to 1.50ct range: core bridal demand window

• Approximately 25 percent at 1.50ct and above: higher margin but slower velocity

High carat weights carry disproportionately greater per-unit carrying cost and depreciation risk. Increase depth in this range only when sales history supports it. For IGI certified loose diamonds from 0.30ct upward, use the certified diamond search to check current availability and pricing by shape and grade.

Step 4: Build Your Monthly Buying Calendar

With shape audit, seasonal peaks, and carat distribution mapped, assign a target stock value and reorder frequency for each month. Your buying calendar has three components:

• Core stock: consistent-selling shapes held at a minimum display quantity every month regardless of season

• Peak additions: the specific shapes and carat ranges you increase depth on during each of the four demand periods

• Reorder trigger points: the stock level at which you place the next order, set to account for the 3 to 5 day delivery window from Antwerp

The €500 minimum order at LabGems allows targeted replenishment of specific shapes — princess cut diamonds for a seasonal window, or heart shaped diamonds for the Valentine's period — without requiring large infrequent orders that inflate your average inventory value and carrying cost exposure.

Step 5: Review and Adjust Quarterly

A 12-month plan is a working document, not a fixed forecast. Review actual sales against projections at the end of each quarter. Ask three questions: which shapes over- or underperformed against forecast? Did any carat ranges show demand shifts you did not anticipate? Are there new categories — lab-grown gemstones or non-certified lab-grown diamonds — that should enter the range?

Quarterly review also aligns your annual plan with changes in lab-grown diamond wholesale pricing, which affect the depreciation component of your carrying cost model. Detailed guidance on managing stock within each quarter is in the Stock Rotation Frameworks guide.

Getting Started

The most practical starting point is the beginning of a new quarter, using the previous 90 days as your sales baseline. Use the certified diamond search for current availability by shape and carat, visit the wholesale buying page for ordering details, or contact the LabGems team directly.

Frequently Asked Questions

Q1. How far in advance should I build stock for seasonal peaks like Valentine’s Day or Christmas?
Plan to have peak stock fully in display approximately 30 to 35 days before each demand window opens. For Valentine’s Day, that means stock confirmed and in display by approximately 20 January. For Christmas, begin building certified diamond stock from the first week of October. This accounts for the 3 to 5 day Antwerp delivery window plus time needed for display preparation and grading report review on arrival.

Q2. What carat weight distribution should I use as a starting point for my stock plan?
A conservative starting allocation for most mid-market European retailers is approximately 40 percent of units in the 0.30ct to 0.70ct range, 35 percent in the 0.70ct to 1.50ct range, and 25 percent at 1.50ct and above. Adjust this based on your actual sales history after the first two quarters. High carat weights carry greater per-unit carrying cost, so increasing depth in that range should always be driven by evidence, not projection.

Q3. How should I handle shapes I have no sales history for?
For shapes being introduced into your range for the first time — radiant cuts, asscher cuts, or princess cuts — set an initial allocation of no more than two to three units and treat the first 90-day cycle as a live test. Track enquiry rate, not just sales: a shape that generates consistent customer interest but no conversion may need a price or positioning adjustment rather than removal.

Q4. How does a 12-month stock plan interact with the 90-day rotation model?
The 12-month plan sets your strategic inventory targets — how much of each shape and carat weight you intend to hold across the year, and when. The 90-day rotation model is the operational tool that runs within that framework, governing day-to-day reorder decisions, velocity checks, and slow-stock actions. During peak windows, the 90-day model’s standard rotation logic is overridden by the seasonal depth requirements set in the annual plan.

Q5. When is the right time to add lab-grown gemstones or coloured diamonds to a stock plan?
Add these categories once your core certified diamond range has at least two full 90-day cycles of velocity data behind it. Lab-grown gemstones and coloured lab-grown diamonds perform well as gifting options in the pre-summer window and as complementary lines during the Christmas peak. Introduce them at a conservative unit allocation and review against the same monthly carrying cost threshold you apply to certified colourless stock.