Invoice Calculator
Build up an invoice with multiple line items, apply discounts and VAT, and get your total instantly.
Results are for general guidance only — not professional advice. Learn more.
How to use this tool
Enter your invoice line items, apply any discount and VAT rate, and instantly see the subtotal, discount amount, VAT, and total.
- Fill in each line item with a description, quantity, and unit price.
- Click Add line item to add more rows (up to 8 total). Use the Remove button to delete a row.
- Enter any Discount % to apply across the whole invoice.
- Set the VAT Rate % — the default is 20% (UK standard rate).
- Read off the subtotal, discount amount, VAT amount, and final total from the results panel.
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Frequently asked questions
How do I calculate an invoice total?
To calculate an invoice total, add up all line item amounts (quantity multiplied by unit price) to get the subtotal. Then subtract any discount amount, add VAT on the discounted subtotal, and the result is the invoice total. The formula is: Total = (Subtotal − Discount) × (1 + VAT rate / 100).
Should VAT be applied before or after discount?
In the UK, VAT should generally be applied after the discount has been deducted. HMRC guidance states that if a prompt payment discount is offered, VAT is calculated on the discounted price even if the customer does not take the discount. For standard discounts, VAT is applied to the net amount after deducting the discount.
What is a line item on an invoice?
A line item is a single row on an invoice representing one product or service. Each line item typically includes a description, the quantity supplied, the unit price, and the line total (quantity multiplied by unit price). Multiple line items are summed to produce the invoice subtotal.
How do I add more line items?
Use the 'Add line item' button below the line items to add additional rows. You can add up to 8 line items in total. To remove a line item, click the Remove button on the right-hand side of that row. The totals update automatically as you make changes.