Split the Bill Calculator

WHAT IT DOES

Split the Bill Calculator is a floating panel that takes the headache out of dividing restaurant tabs, group expenses, or shared costs. Enter the total bill amount, the number of people, a tip percentage, and any additional tax amount—the panel instantly calculates the per-person share, breaking it down into base amount, tax per person, tip per person, and the final total per person. An optional "round up" toggle rounds each person's share up to the nearest dollar, with the overage amount shown separately so you know exactly how much extra was added. You can then insert the per-person total directly into any editable field on the page (input, textarea, or contenteditable) with one click, or copy it to your clipboard. Perfect for splitting dinner bills, group gifts, shared subscriptions, or any multi-person expense.

WHERE IT RUNS

The panel overlays any website that loads the BotGentz extension—whether you're on a bill-splitting app, a group chat, a spreadsheet, a note-taking tool, or any other web page. It works on all modern Chromium‑based browsers (Chrome, Edge, Brave, Arc) and Firefox. The script injects a self‑contained UI element that does not interfere with the host page's layout, styles, or JavaScript execution. It runs client‑side only, with no external API calls or cloud dependencies.

HOW TO USE

After installing the free BotGentz extension, visit any page and click the extension icon to activate the panel. The first time you use Split the Bill Calculator, it will appear as a draggable widget near the bottom‑right corner of your viewport. To split a bill:

- Enter the total bill amount in the "Total bill amount ($)" field.

- Enter the number of people in the "Number of people" field.

- Enter a tip percentage in the "Tip percentage (%)" field (use 0 for no tip).

- Enter any tax amount in the "Tax amount ($)" field (use 0 if none).

The panel updates all breakdown figures live—base per person, tax per person, tip per person, and total per person—as you type. Toggle "Round up each share to nearest dollar" to apply rounding; the overage amount appears below the total. To use the result:

- Click "Insert Per-Person Total into Active Field" to paste the total into whichever input, textarea, or contenteditable element you have focused on the page.

- Click "Copy Per-Person Total to Clipboard" to copy the total to your system clipboard for pasting anywhere.

The panel remembers your last used tip percentage, tax amount, and round-up preference across sessions.

BIDIRECTIONAL DEPENDENCY RESOLVER WITH ROUNDING STATE MANAGEMENT

Unlike simple calculators that recompute everything on every keystroke and lose precision, this panel uses a bidirectional dependency resolver that tracks each input's version and recalculates only the affected outputs. The engine constructs a directed graph where nodes represent input fields (bill, people, tip, tax) and output displays (base, tax, tip, total, overage). When an input changes, the engine marks all dependent nodes as stale and recomputes them in topological order. The rounding feature adds a special state node that toggles the rounding behavior—when enabled, the total node passes its value through a ceil() function and computes the overage as the difference. The engine also implements precision anchoring: all intermediate calculations are performed at full floating-point precision, and only the final display values are rounded to two decimal places. This prevents cumulative rounding errors that plague naive calculators, ensuring that rounding up a dollar amount and then subtracting the rounded total from the original sum yields the correct overage down to the cent. The system also includes a debounced update mechanism that batches rapid keystrokes into a single recalculation cycle, maintaining smooth performance even during fast typing.

THE PANEL

- Drag: Click and hold the panel's header bar to move it anywhere on the screen.

- Per‑site position: The panel stores its last position separately for each domain (e.g., different positions for Google Docs vs. Splitwise) using the browser's localStorage, keyed by hostname.

- Snap: When dragged near any edge of the viewport, the panel snaps to that edge with a 16px margin for a clean, docked feel.

- Collapse: Click the "−" button in the header to collapse the panel to a compact title bar, preserving all current values. Click "+" to expand it back.

- Resize: Drag the bottom‑right corner handle to resize the panel from 280px to 600px wide and 200px to 500px tall; the layout adapts responsively.

- Escape: Press the Escape key while the panel is focused to close it entirely (you can reopen it from the extension toolbar).

PLEASE NOTE

This script requires the free BotGentz extension to run—it is not a standalone bookmarklet or user script. Websites frequently update their DOM structures and security policies; while we strive to keep the panel functional across thousands of sites, occasional updates may be needed. The calculator performs all operations entirely in your browser—no data is sent to any server, and no cookies or tracking identifiers are used. Your bill amounts, tip preferences, and tax figures remain private to your local session and are persisted only via GM_setValue (the extension's local storage) for convenience, not shared across devices or sessions. We recommend verifying critical splits with your group members, as rounding preferences and currency conventions may vary.