What is an invoice calculator?

An invoice calculator works out the amounts on an invoice: each line total, the net subtotal, the VAT per rate and the gross total you are asked to pay. It lets you confirm that the figures printed on a document actually add up.

How is the gross invoice total calculated?

Each line is quantity multiplied by unit price. Those line totals are added together to give the net subtotal. VAT is calculated per VAT rate on the net amount in that rate group, and the net subtotal plus the total VAT gives the gross total.

Can I enter invoice items manually?

Yes. You can start with an empty invoice and type the description, quantity, unit, unit price and VAT rate for each line. Totals update as you type.

Can invoice lines use different VAT rates?

Yes. Lines are grouped by VAT rate, each group gets its own net and VAT amount, and the groups are summarised before the gross total.

Does the invoice calculator give tax advice?

No. It is a calculation tool. Which VAT rate applies to a given supply is a tax question, so check anything that affects a tax return or a payment with a qualified accountant.

Invoice calculator online

Calculate line totals, the net subtotal, VAT per rate and the gross total of an invoice. Type the figures in yourself, or upload an invoice photo or PDF, review what was read and calculate from there.

Open the invoice calculator Check an invoice

What an invoice calculator does

An invoice is a short chain of arithmetic: every line is priced, the lines add up to a net amount, VAT is applied to that net amount, and the two together make the gross total. An invoice calculator performs that chain for you and keeps each intermediate figure visible, so you can see where a total comes from instead of trusting a single number at the bottom of a page.

That matters most when an invoice arrives with many lines, mixed VAT rates or awkward quantities, where a small rounding or transcription mistake is easy to miss.

How to calculate an invoice total

1Line total: multiply quantity by unit price for each line.
2Net subtotal: add all line totals together.
3VAT: group the lines by VAT rate and apply each rate to the net amount of its group.
4Gross total: add the net subtotal and the total VAT.
5Compare: check the gross total you calculated against the total printed on the invoice.

Quantity × unit price

A line for 10 units at 100 Kč is 1,000 Kč net. Watch the unit: a price quoted per hour, per kilogram or per thousand pieces has to be multiplied by a quantity in the same unit, and a mismatched unit is one of the more common sources of an unexpected total.

Net, VAT and gross

Net is the amount before tax, VAT is the tax charged on it, and gross is what is actually payable. VAT is calculated on the net amount, not on an already-gross figure — applying a rate twice inflates the total.

Different VAT rates on one invoice

Many invoices mix rates, for example a standard rate on goods and a reduced rate on a service. Each rate is calculated on its own subtotal and the results are added. A single blended percentage applied to everything will usually give a slightly different answer.

A worked example

The simplest possible single-line invoice, shown step by step:

Illustrative example — not a real invoice

Quantity: 10
Unit price: 100 Kč
Net subtotal: 1,000 Kč
VAT 21%: 210 Kč
Gross total: 1,210 Kč

This example is illustrative only. Use your own figures and the VAT rate that actually applies to your supply.

Manual entry or upload

Entering an invoice manually

Start from an empty invoice and add lines one at a time: description, quantity, unit, unit price and VAT rate. The net, VAT and gross for each line, the VAT summary and the grand total all update while you type, so you can build a total up piece by piece.

Uploading an invoice

You can also upload the invoice as a photo or a PDF. The document is read, the supplier, invoice number, dates, currency and line items are filled in for you, and every field stays editable.

Reviewing what was read

Automatic reading is not perfect, particularly on a creased paper invoice or a low-light photo. Fields the system is less sure about are marked for you to confirm. Review the extracted values before you rely on the calculation.

Checking the calculation

Once the lines are correct, the calculated total is compared with the total stated on the document. A difference is shown with the arithmetic behind it, so you can decide whether it is a rounding convention or a genuine error worth querying.

Frequently asked questions

What is an invoice calculator?: An invoice calculator works out the amounts on an invoice: each line total, the net subtotal, the VAT per rate and the gross total you are asked to pay. It lets you confirm that the figures printed on a document actually add up.
How is the gross invoice total calculated?: Each line is quantity multiplied by unit price. Those line totals are added together to give the net subtotal. VAT is calculated per VAT rate on the net amount in that rate group, and the net subtotal plus the total VAT gives the gross total.
Can I enter invoice items manually?: Yes. You can start with an empty invoice and type the description, quantity, unit, unit price and VAT rate for each line. Totals update as you type.
Can invoice lines use different VAT rates?: Yes. Lines are grouped by VAT rate, each group gets its own net and VAT amount, and the groups are summarised before the gross total.
Does the invoice calculator give tax advice?: No. It is a calculation tool. Which VAT rate applies to a given supply is a tax question, so check anything that affects a tax return or a payment with a qualified accountant.

ChargeAlign is a calculation and review tool. It does not provide tax, accounting or legal advice, and results should be verified against your own records and, where it matters, with a qualified professional.

Related calculators and checks

VAT calculator

Add VAT to a net price or take VAT back out of a gross price.

Invoice calculator from a photo

Upload a photo or PDF, review what was read, then calculate.

Invoice checker

Go through an invoice field by field before you pay it.

Invoice discrepancy checker

See where a stated amount differs from the calculated amount.