Auction Site Bid Increment Calculator

WHAT IT DOES

This userscript helps auction bidders make smarter bidding decisions by calculating bid increments and visualizing the bid ladder. It scans auction and bidding site pages—eBay, GunBroker, Bonanza, live auction platforms, and similar sites—to extract the current bid price, minimum bid increment, and next bid amount. It displays a panel with the bid increment table, the next minimum bid, and the impact of bidding strategies. The script includes a "Bid Ladder Simulator" where you can enter your maximum bid and see the full sequence of bids that would occur, showing exactly how many bids it takes to reach your target and what the final price would be. It also highlights optimal bid amounts to avoid overpaying.

WHERE IT RUNS

The script works on auction and bidding site pages—eBay, GunBroker, Bonanza, live auction platforms, and similar sites. It runs entirely within your browser, reading only the visible content of the current page. It does not track your browsing history, access other tabs, or send any data externally. All calculations are performed locally using built-in bid increment tables.

HOW TO USE

After installation, open the panel by clicking the tool's icon in the BotGentz sidebar. The script auto-scans auction pages on load (toggle this on/off). Choose your display mode—"Panel only" shows the calculator in the panel, or "Both" adds a badge. Toggle "Show increment table" to display the full bid increment schedule. Click "Scan auction" to manually analyze the page. The panel displays the current price, next bid, increment, and bid count. Use the Bid Ladder Simulator: enter your maximum bid and click "Calculate" to see the full bid ladder showing each incremental bid and the final winning amount. Use "Clear calculator" to remove the display.

THE TECHNICAL MECHANISM

This script uses a standard bid increment table based on eBay-style increments: $0.01–0.99 → $0.05, $1.00–4.99 → $0.25, $5.00–24.99 → $0.50, $25.00–99.99 → $1.00, $100–249.99 → $2.50, $250–499.99 → $5.00, $500–999.99 → $10.00, $1,000–2,499.99 → $25.00, $2,500–4,999.99 → $50.00, $5,000–9,999.99 → $100.00, $10,000+ → $250.00. The script extracts the current price from the page using regex patterns and common selectors like .current-price, .bid-price, and [class*="price"]. It calculates the next bid by applying the increment table: nextBid = ceil((currentPrice + 0.01) / increment) * increment. For the bid ladder, it iteratively calculates the next bid from the current price until it reaches or exceeds the user's maximum bid, recording each step. The ladder shows the bid number, amount, and increment for each step, highlighting the final winning bid. The increment table is displayed as a reference for the user.

THE PANEL

The panel is draggable anywhere on the screen and remembers its position between sessions. It can be collapsed to a small floating bubble to minimize distraction, and expanded again with a single click. The panel's width can be adjusted, and pressing the Escape key closes it instantly. All settings—display mode, show table, and auto-scan—are persisted locally using GM_setValue, so your preferences remain intact across page reloads and browser restarts.

PLEASE NOTE

This userscript requires the free BotGentz extension to function. The script is designed for auction and bidding sites; it may work on other sites with similar bid structures but is not guaranteed. The bid increment table is based on eBay's standard increments; other auction platforms may use different increment rules. The extraction relies on the current text patterns on each site—if a site updates its UI, the script may need to be updated. The bid ladder is a simulation based on the current price and increment rules; actual bidding may differ due to other bidders and bid timing. The script does not access your account or API; it only reads what is visible on the page. No data from your browsing is stored or transmitted anywhere—all processing occurs entirely in your browser.