Invoice Calculator
Calculate invoice totals from multiple line items, with tax, discount, and shipping applied. Add as many line items as you need — the subtotal, tax, discount, and grand total update as you type.
How Invoice Totals Work
An invoice total is built in four steps: line item subtotal, tax addition, discount subtraction, and shipping addition. Order matters — tax is calculated on the pre-discount subtotal in most jurisdictions, then the discount is subtracted, then shipping is added.
Some countries and industries apply tax after the discount. If that is your case, apply the discount to the subtotal first, then calculate tax on the discounted amount. Both approaches are valid — follow the rule in your jurisdiction.
Invoice Formulas
Line Item Total = Quantity × Unit Price
Subtotal = Sum of all Line Item Totals
Tax Amount = Subtotal × (Tax Rate ÷ 100)
Discount Amount = Subtotal × (Discount Rate ÷ 100)
Grand Total = Subtotal + Tax − Discount + Shipping
A negative grand total is possible if the discount exceeds subtotal plus tax plus shipping — usually a data entry error.
Worked Example
Two line items: 2 × $100 = $200 and 1 × $150 = $150.
Subtotal = $200 + $150 = $350
Tax at 10% = $350 × 0.10 = $35
Discount at 0% = $0
Shipping = $0
Grand Total = $350 + $35 − $0 + $0 = $385
Frequently Asked Questions
Should tax be applied before or after a discount?
In most jurisdictions, tax is calculated on the discounted amount — the customer only pays tax on what they actually pay. Some industries and countries apply tax before the discount. This calculator applies tax on the pre-discount subtotal, then subtracts the discount. Adjust the order if your local rules require otherwise.
Is shipping taxable?
It depends on the jurisdiction. In many US states, shipping is taxable if it is not separately stated or if the item being shipped is taxable. In the UK and EU, delivery charges are usually taxable at the same rate as the goods. Check your local rules.
What is the difference between an invoice and a receipt?
An invoice is a request for payment sent before the customer pays. A receipt is proof of payment issued after. An invoice lists what was sold and the amount due; a receipt confirms that payment was received.
Can I include a discount on an invoice?
Yes. A discount reduces the total amount due. It can be expressed as a percentage or a flat amount. Whichever form you use, state it clearly on the invoice so the customer can see what was charged and what was deducted.
What should an invoice include?
A standard invoice includes: invoice number, invoice date, due date, seller details (name, address, tax ID), buyer details, itemized list of goods or services with quantities and prices, subtotal, tax, discount if any, shipping if any, and grand total. Some jurisdictions also require payment terms and bank details.
What is a good payment term for an invoice?
Net 30 (payment due in 30 days) is the most common business-to-business term. Net 15 and Net 45 are also common. For small transactions or new customers, "due on receipt" is safer. Longer terms increase the risk of late payment and hurt your cash flow.