Subtotal

The subtotal is a checkpoint in the invoice maths. The line items each contribute a quantity times a unit price, and those line totals add up to the subtotal. From the subtotal, the invoice applies any invoice-level discount, then calculates tax on the discounted amount, then adds the tax to produce the total. Showing the subtotal explicitly lets the buyer's accounting system verify each step without having to back-calculate from the total.

Order of operations matters more than it looks. The convention is subtotal → discount → tax → total, with discounts reducing the taxable base. Some sellers apply discounts after tax, which slightly changes the maths and creates more work on the VAT side (because reported tax has to match the discounted invoice). Stating the order on the invoice (or on the contract) removes ambiguity in advisor-grade audits.

For invoices with both taxable and tax-exempt line items, you generally see two subtotals: one for the taxable items (which has tax applied to it) and one for the exempt items (which does not). The grand total still combines them, but the breakdown makes the buyer's input-tax-credit calculation straightforward.