How It Works

Invoice calculation engine

All amounts are calculated with decimal arithmetic, not floating point. Money values are stored as exact decimals, so combinations like 2.5 × 19.99 produce the same result in the live preview, the PDF and a saved draft — with no 0.1 + 0.2 rounding surprises.

• Each line amount is quantity × rate, rounded half-up to the currency’s decimal places
• The subtotal is the sum of the rounded line amounts
• Discounts can be a percentage or a fixed amount, and never exceed the subtotal
• When different lines use different tax rates, the discount is allocated proportionally across the tax groups

Currency formatting and rounding

Each of the supported currencies has a defined number of minor units: USD and EUR use two decimals, JPY uses zero. Formatting uses the platform’s internationalization support, so amounts are displayed and printed consistently. Rounding is deterministic half-up rounding applied at the currency’s precision.

Tax modes

In exclusive mode, tax is calculated on the discounted amount and added on top of it. In inclusive mode, your prices already contain tax: the engine extracts the tax portion from the discounted amount, so the total does not change. Shipping is added after tax.

PDF generation

The PDF is generated in your browser with a text and vector layout — it is not a screenshot of the page. That means the text is selectable and searchable, the file stays small, and the invoice prints cleanly at A4 or US Letter size. The PDF library is only loaded when you click “Download PDF”, so the first page load stays fast. Invoices with many line items continue onto additional pages, repeating the table header.

Local data storage

“Save Draft” stores the invoice in your browser’s storage on this device. Drafts are not uploaded anywhere and are not visible to us. You can delete saved drafts at any time with “Delete Saved Drafts”. If your browser blocks storage — for example in some private windows — the generator still works; only saving drafts and restoring them is unavailable.

Privacy

Your invoice content — business details, client details, items, amounts, notes and logo — is processed entirely in your browser. It is never sent to a server, and it is never sent to analytics. Usage analytics, when enabled, record anonymous product events only, such as “PDF downloaded” or “item added”, without any invoice content or personal data.

Limitations

• No currency conversion: pick the currency you invoice in
• Shipping is not taxed in this version
• Invoice requirements and tax rules vary by country — this tool does not provide legal or tax advice
• Drafts live on one device and one browser; they are not synced between devices