Invoice Calculator

A proper invoice calculation follows a specific order: line items (quantity × unit price) are summed into a subtotal. Then discounts are applied (percentage or fixed amount off the subtotal). Tax is calculated on the post-discount amount. Finally, shipping or additional fees are added to reach the total.

Getting the order wrong — like calculating tax before discount — results in overcharging. Different jurisdictions have different rules about what's taxable, at what rate, and whether shipping is taxed. This tool follows the most common convention: subtotal → discount → tax → shipping → total.

The copy feature outputs a clean text breakdown suitable for pasting into emails, invoices, or accounting software. For freelancers and small businesses, this eliminates spreadsheet setup for quick quotes and estimates while keeping the math transparent and error-free.