Discount before or after tax: getting invoice order right
Why the sequence of discount, tax and shipping changes an invoice total, with worked examples and the convention this calculator follows.
Why the order changes the total
An invoice is not just a pile of numbers added together; the sequence in which you apply a discount, tax and shipping decides the final figure. A discount taken before tax lowers the amount that tax is charged on, which reduces both the tax and the total. The same discount applied after tax leaves the tax untouched and only trims the final line. On a large invoice those two paths can differ by a meaningful amount, so agreeing the order up front avoids disputes with clients and auditors.
The convention this calculator uses
This tool follows the most common commercial sequence: subtotal first, then discount, then tax, then shipping. It sums every line item into a subtotal, subtracts the percentage discount to produce a taxed base, charges the tax percentage on that base, and adds flat shipping at the very end. Shipping is not taxed here. That ordering matches how most storefronts and accounting packages present a receipt, where the customer sees a discount lowering the goods before sales tax is calculated on the reduced price.
A worked example you can check
Take two items, two units at fifty dollars and one at thirty, for a subtotal of one hundred and thirty dollars. A ten percent discount removes thirteen dollars, leaving a taxed base of one hundred and seventeen. Eight percent tax on that base is nine dollars and thirty six cents. Add five dollars of shipping and the grand total is one hundred thirty one dollars and thirty six cents. If tax had been charged on the full subtotal instead, it would have been ten dollars and forty cents, over a dollar higher, which shows why the discount belongs before the tax.
Rounding and reconciliation
Percentages rarely land on whole cents, so each component is rounded to two decimal places before it is displayed. Rounding every part independently and then summing can occasionally drift by a cent compared with rounding only the final total, which is why this calculator is built so the shown parts reconcile to the grand total. When you copy figures onto a real invoice, keep the same rounding rule throughout so the line items, tax and total always foot to the penny.