GMROII Batch Calculator

A browser-based tool for independent bookstores to analyze inventory performance across multiple titles using Gross Margin Return on Inventory Investment (GMROII) — based on Shatzkin's The Mathematics of Bookselling.

Features

• CSV Upload — drag & drop or browse; auto-detects comma/semicolon separator and 5 or 6-column format
• Portfolio Summary — aggregate metrics: total inventory at cost, weighted GMROII, annual gross margin, average stock turn, underperforming titles count
• Sortable Table — 12 columns with color-coded rows (red = GMROII < 1, green = GMROII >= 2); click headers to sort
• Expandable Detail Panels — click any row to open a full dashboard per title: 8 metric cards, earning power decline chart, order quantity comparison table
• Editable Parameters — per-title order quantity slider and invoice payment days; global reorder frequency and lead time
• Optimal Order Qty — automatically calculated to cover demand during reorder cycle + lead time
• Multilingual Lexicon — parameter definitions in Romanian, English, German, and French
• CSV Export — download results with all calculated metrics

CSV Format

6-column (with title):

ISBN,Title,Purchase Price,Sale Price,Units Sold,Current Stock
978-0-06-112008-4,To Kill a Mockingbird,8.40,14.00,12,4

5-column (without title):

ISBN,Purchase Price,Sale Price,Units Sold,Current Stock
978-0-06-112008-4,8.40,14.00,12,4

• Units Sold = copies sold in the last 4 weeks
• Separator: , or ; (auto-detected)

Files

File	Description
gmroii-batch-calculator.html	Main application (single HTML file, no dependencies)
gmroii-sample-150.csv	Sample dataset with 150 titles for testing
gmroii-calculator.html	Single-title GMROII calculator (standalone)

Usage

1. Open gmroii-batch-calculator.html in any modern browser
2. Click Load Sample Data to test with built-in data, or upload a CSV file
3. Adjust Reorder Frequency and Lead Time as needed
4. Click any row to explore detailed metrics
5. Click Export Results CSV to download

Key Metrics Explained

• GMROII = Margin per $ Invested × Stock Turn — dollars of gross margin per dollar invested in inventory per year
• Stock Turn = Annual sales at cost / Average inventory at cost
• Recovery = Days for sales revenue to cover the order cost
• Earning Power Decline = How GMROII drops the longer a copy sits unsold

License

This project is licensed under the GNU General Public License v3.0 — see LICENSE for details.