How the total is calculated
Each line is quantity times unit price, rounded to the cent, so the lines on the PDF always add up to the subtotal shown. The discount comes off the subtotal, then tax is charged on the discounted amount.
Line amount = quantity × unit price
Subtotal = sum of line amounts
Taxable amount = subtotal − discount
Tax = taxable amount × tax rate ÷ 100
Total = taxable amount + tax
Worked example
A designer bills a logo package at 1 × $1,200.00 and two business card layouts at 2 × $150.00. The subtotal is $1,500.00. A 10% loyalty discount takes off $150.00, leaving $1,350.00. Sales tax at 8.25% on that is $111.375, which rounds to $111.38. The client owes $1,461.38.
Tax is rounded half a cent up, the way a calculator and most accounting software do it. Some tax authorities have their own rounding rules for specific cases, so check with yours if a single cent matters.
What to put on an invoice
There is no single legal template in the US, but an invoice is one of the records the IRS lists for proving gross receipts, so make it complete. In the UK, the government's guide to what an invoice must include lists these items:
| Item | Where it goes in this form |
|---|---|
| A unique invoice number | Invoice number |
| Your business name, address and contact details | Your business |
| The customer's name and address | Bill to |
| A clear description of what you are charging for | Line items |
| The date of the invoice | Issue date |
| The date the goods or service were provided | Add it to the line description or the notes |
| The amounts charged, any VAT, and the total owed | Line items, tax rate and total |
The same guide adds that sole traders using a business name must also show their own name and an address where legal documents can be delivered, and limited companies must use their full registered company name. Businesses registered for VAT have extra rules for VAT invoices, including showing your VAT number; this tool does not produce a full VAT invoice on its own, so add your VAT number to the notes and check HMRC's guidance.
Tips that get invoices paid faster
- Put the due date and how to pay (bank details, a payment link, or who to make checks out to) in the notes. Unclear payment instructions are a common reason invoices sit unpaid.
- Send the invoice as soon as the work is done, while the client still remembers the value.
- Use a fresh invoice number every time and keep a copy of every PDF you send.
- If the client has a purchase order number, add it to the notes so their accounts team can match it.
Your data stays on your device
The PDF is generated in your browser with the open-source pdf-lib library. Nothing you type is uploaded. The form is saved in this browser's local storage so it is still there when you come back; use "Delete saved data" on a shared computer.
Questions people ask
Is this invoice generator really free, and do I need an account?
Yes, it is free and there is no sign-up. The PDF is built in your browser. Nothing you type is sent to our server; the form is saved only in this browser so you can come back to it.
Is tax charged before or after the discount?
After. The discount comes off the subtotal first, and tax is charged on what is left. A $1,000 subtotal with a 10% discount and 8% tax is $1,000 − $100 = $900, plus $72 tax, for a total of $972.
What invoice number should I use?
Any system works as long as every invoice gets a unique number and you never reuse one. A prefix and a running number, such as INV-0001, INV-0002, is the simplest. When you start a new invoice here, the number goes up by one automatically.
What payment terms should I put on an invoice?
Net 30 (payment due 30 days after the invoice date) is the most common for business clients, with Net 14 or Net 7 common for freelancers. Whatever you choose, write it in the notes with how to pay you, such as your bank details or a payment link.
Why do some characters show as a question mark in the PDF?
The PDF uses the standard Helvetica font, which covers English and Western European letters, the euro and pound signs and common punctuation. Emoji and scripts such as Chinese, Arabic or Cyrillic cannot be drawn with it, so they are replaced with a question mark rather than breaking the file.
Can I add my logo?
Not yet. The invoice uses your business name as a text heading, which keeps the file small and prints cleanly in black and white.