How the totals are calculated
Each line item's amount is quantity × unit price, and the subtotal is the sum of those lines. The order of the next steps matters, because it changes the tax you charge. The tool applies the discount first (as a percentage of the subtotal or as a flat amount), then applies the tax rate to the discounted total:
- Subtotal = sum of (qty × unit price)
- Discount = subtotal × discount% (or the flat amount you enter)
- Taxable amount = subtotal minus discount, never below zero
- Tax = taxable amount × tax rate
- Total due = taxable amount + tax
Charging tax on the discounted price is the usual treatment for a simple price reduction, but rules vary by jurisdiction and by discount type. Confirm yours with an accountant or tax authority.
A worked example
| Line | Qty | Unit price | Amount |
|---|---|---|---|
| Logo design | 1 | $600.00 | $600.00 |
| Brand guide pages | 8 | $50.00 | $400.00 |
| Revisions (hours) | 3 | $75.00 | $225.00 |
The subtotal is $1,225.00. A 10% early-client discount removes $122.50, leaving a taxable amount of $1,102.50. At 8% sales tax the tax is $88.20, so the total due is $1,190.70. Had tax been applied before the discount, you would have charged $98.00 in tax, a difference of $9.80. For percentage-based work, the sales tax calculator is useful for checking a figure.
What the PDF contains
The PDF includes your details and the client's, the invoice number (default INV-0001), issue and due dates (due defaults to 14 days after issue), the itemized table, discount and tax lines, the total and your notes. You can choose A4 or US Letter and one of seven currencies: USD, EUR, GBP, INR, AUD, CAD and JPY. The PDF is built with a standard font that cannot draw the rupee glyph, so INR amounts print as "Rs.". The file is generated locally with pdf-lib, and a draft of your entries is kept in your browser's local storage so you can come back later. Use "Clear draft" to wipe it on a shared computer.
Common mistakes
- Reusing an invoice number. Duplicate numbers confuse bookkeeping and can raise questions in an audit. Change the number for every new invoice.
- Vague line items. "Services" invites disputes. Name the work, the quantity and the rate.
- No due date or payment terms. Put the due date and accepted payment methods in the notes.
- Mixing tax-inclusive and tax-exclusive prices. This tool treats unit prices as tax-exclusive and adds tax at the end. If your prices already include tax, work backwards first with the GST calculator.
- Wrong tax registration details. Some regions require your tax ID on the invoice. Add it to your details or notes.
For a full checklist of required fields and payment-term wording, read the guide How to Make a Professional Invoice, and for tax-inclusive pricing see How to Calculate GST on an Invoice. To check what a job earns you, try the profit margin calculator.