Invoice Calculator
Add line items, discounts, tax, and payments to get the invoice total and balance due.
How is invoice calculator worked out?
An invoice total is the subtotal of all line items, minus any discount, plus tax on the discounted amount, plus shipping. The balance due is that total minus anything the customer has already paid.
Invoice Calculator
Balance due
$0.00
- Invoice total
- $0.00
- Tax
- $0.00
Show the working
| Subtotal (3 line items) | $0.00 |
| Discount | -$0.00 |
| Taxable amount | $0.00 |
| Tax at 0% | $0.00 |
| Shipping | $0.00 |
| Invoice total | $0.00 |
| Less amount paid | -$0.00 |
| Balance due | $0.00 |
The order of operations is what trips most invoices up. Discount comes off the subtotal first, tax is charged on what is left, and shipping is added afterwards — apply tax before the discount and you overcharge, apply it after shipping and you may tax a delivery charge that should not be taxed. This calculator does it in the conventional order and shows each step.
The formula
Subtotal = Σ (quantity × rate)
Discount = subtotal × discount % (or a fixed amount)
Taxable amount = subtotal − discount
Tax = taxable amount × tax rate
Total = taxable amount + tax + shipping
Balance due = total − amount already paidTax is applied to the discounted subtotal, which is the usual treatment: a discount reduces the value of the supply, so it reduces the tax with it. Shipping sits outside the tax base here — some jurisdictions do tax delivery, so check your local rules if delivery is a large part of the invoice.
Why discount before tax matters
If you tax the full subtotal and then discount the result, the customer pays tax on money they were never charged, and your tax filing overstates what you collected. Taking the discount off first keeps the tax proportional to the value actually supplied. The exception is a discount offered conditionally after the invoice is issued — an early-payment discount, for example — which most regimes treat differently because at the point of invoicing you do not yet know whether it will be taken.
Recording deposits correctly
A deposit already received belongs in the amount-paid field, not as a negative line item. Showing it as a negative line reduces your subtotal, which reduces the tax you report on a supply you actually made in full. Keeping it below the total leaves the value of the supply and the tax intact, and shows the customer exactly what is left to pay.
Frequently asked questions
How do you calculate an invoice total?
Multiply each line item's quantity by its rate and add them up to get the subtotal. Subtract any discount, then apply the tax rate to what remains. Add shipping to get the invoice total, and subtract any payments already received to get the balance due.
Is tax calculated before or after a discount?
After. A discount reduces the value of what you supplied, so tax is charged on the discounted amount. Applying tax to the full subtotal and then discounting overcharges the customer and overstates the tax you owe.
Should shipping be taxed?
It depends on your jurisdiction. Some tax regimes treat delivery as part of the taxable supply and some do not, and the answer can change depending on whether delivery is optional or separately stated. This calculator leaves shipping outside the tax base — check your local rules if delivery is a significant part of the invoice.
Put the number on an invoice
The free invoice generator builds the document around your figures — line items, tax, payment terms — and downloads a print-ready PDF. No signup required.
Related calculators
- Hourly Invoice CalculatorTurn hours and hourly rates into an invoice total, with expenses, discounts, tax, and deposits.
- Invoice Discount CalculatorApply a percentage or fixed discount and see the new invoice total, with optional tax after the discount.
- Sales Tax CalculatorAdd sales tax to a pre-tax amount or remove tax from a tax-inclusive total using any rate.
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