Diamond Price Index Methodology
How TheDiamondPrice.com calculates diamond values, collects market data, and scores the best deals
Last Updated: February 11, 2026
Data Coverage: 500,000+ certified diamonds
Update Frequency: Real-time (every 24 hours)
Retailers Tracked: 50+ authorized jewelers
Data Collection Process
1. Source Selection
We aggregate real-time pricing data exclusively from authorized diamond retailers who meet our quality standards:
- Certification Requirement: Only retailers offering GIA, IGI, or AGS certified diamonds
- Transparency Standards: Clear pricing with full diamond specifications
- Inventory Verification: Real-time availability confirmed via API or SFTP feeds
- Reputation Assessment: Established retailers with verified customer reviews
2. Data Update Frequency
Our system updates diamond pricing data every 24 hours through automated processes:
- SFTP Feeds: Direct vendor feeds with complete inventory updates
- API Integrations: Real-time price changes from API-enabled retailers
- Data Validation: Automated verification of certification numbers and specifications
- Duplicate Detection: Cross-vendor matching to identify the same diamond listed multiple times
3. Quality Standards
Only certified diamonds meeting specific criteria are included in our index:
- Certification: GIA (Gemological Institute of America), IGI (International Gemological Institute), or AGS (American Gem Society)
- Carat Range: 0.25ct to 5.0ct (covering 99% of engagement ring purchases)
- Cut Quality: Fair to Excellent (for round diamonds)
- Color Range: D through K (colorless to faint yellow)
- Clarity Range: FL (Flawless) through SI2 (Slightly Included)
Price Scoring Algorithm
How We Calculate Value Scores
Our proprietary Value Score (1-5 stars) compares each diamond's price to the market median for identical specifications:
Scoring Methodology:
| Score | Label | Price vs. Market Median |
|---|---|---|
| ⭐⭐⭐⭐⭐ (5 Stars) | Best Deal | 15%+ below market median |
| ⭐⭐⭐⭐ (4 Stars) | Great Value | 8-15% below median |
| ⭐⭐⭐ (3 Stars) | Fair Price | Within 8% of median |
| ⭐⭐ (2 Stars) | Above Average | 8-15% above median |
| ⭐ (1 Star) | Overpriced | 15%+ above median |
Factors Included in Comparison
Our algorithm matches diamonds based on these exact specifications:
- Carat Weight: Matched within 0.05ct range
- Color Grade: Exact match (e.g., G color compared only to G color)
- Clarity Grade: Exact match (e.g., VS2 compared only to VS2)
- Cut Quality: Exact match for round diamonds
- Shape: Same shape (round, princess, oval, etc.)
- Certification Lab: GIA, IGI, and AGS weighted slightly differently
- Fluorescence: None, Faint, Medium, or Strong
- Diamond Type: Natural vs. Lab-Grown (compared separately)
Market Median Calculation
The market median is calculated using a 90-day rolling average to smooth out short-term price fluctuations while capturing actual market trends. This approach:
- Reduces impact of temporary promotions or outlier pricing
- Reflects true market value based on sustained pricing patterns
- Updates daily as new data enters and old data ages out
- Uses statistical median (not mean) to minimize impact of extreme prices
Diamond Price Index
TheDiamondPrice.com publishes a monthly Diamond Price Index that tracks average price-per-carat across different quality levels and shapes.
Index Calculation Method
Our index uses weighted averages based on:
- Sample Size: Minimum 100 diamonds per category for statistical validity
- Transaction Weighting: More heavily weighted toward "good value" diamonds that buyers actually purchase
- Quality Normalization: Adjusted for color/clarity distribution to ensure fair comparison
- Outlier Removal: Extreme prices (top/bottom 2%) excluded to prevent skewing
Limitations & Disclaimers
Important Limitations:
- Retail Listings Only: Our data reflects advertised retail prices, not final transaction prices (which may include negotiation or discounts)
- Availability Disclaimer: Diamond availability is subject to real-time changes; listed diamonds may sell before you complete your purchase
- Custom & Estate Excluded: Our index does not include custom-made diamonds, estate jewelry, or private sales
- No Physical Inspection: We rely on certification reports; we do not physically inspect diamonds
- Market Conditions: Diamond prices fluctuate based on supply/demand; past trends do not guarantee future prices
- Vendor Independence: While we track prices from affiliate partners, our scoring algorithm is entirely objective and data-driven
Our Commitment to Transparency
TheDiamondPrice.com is committed to providing accurate, unbiased diamond price intelligence:
- No Price Manipulation: We do not alter prices or scores based on affiliate relationships
- Algorithm Objectivity: Our value scoring is fully automated based on mathematical comparison to market median
- Data Integrity: We maintain strict data quality standards and remove obviously incorrect listings
- Methodology Updates: Any changes to our methodology are documented and dated on this page
- Independent Research: Our market analysis and trends are based solely on data, not vendor influence
Questions About Our Methodology?
We believe in complete transparency. If you have questions about how we calculate diamond prices or score value, please contact us:
Email: [email protected]
For media inquiries: [email protected]
Methodology Version History:
- v2.1 (February 2026) - Added fluorescence weighting to comparison algorithm
- v2.0 (January 2025) - Implemented 90-day rolling median calculation
- v1.5 (June 2024) - Expanded to include lab-grown diamond index
- v1.0 (January 2024) - Initial methodology published