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How to Write an Invoice

6 min read · Updated September 26, 2026 · by Thomas M, Registered Investment Adviser (South Carolina)

How to Write an Invoice – feature image

A good invoice is clear, complete and easy to pay. This guide lists what to include, explains the calculations behind the totals and shares a few habits that get invoices paid on time.

What to include

  • Your name, business and address; the client’s details.
  • A unique invoice number and the issue and due dates.
  • A description of each item or service, with quantity and unit price.
  • Subtotal, any discount, tax and the total due.
  • Payment methods, bank details and terms (late fees, deadlines).
  • Tax registration number if you charge VAT, GST or sales tax.

The calculations

Line amount = quantity × unit price. Subtotal = sum of lines. Discount = subtotal × %. Tax = (subtotal − discount) × %. Total = subtotal − discount + tax + shipping. Example: design 1 × 1,200, hosting 1 × 180 and 3 revisions at 45.50 give £1,516.50 before 20% VAT of £303.30, a total of £1,819.80.

Getting paid faster

  • Invoice promptly, as soon as the work is delivered.
  • State the due date and terms clearly (“due in 14 days”).
  • Make paying easy: bank details, a link or a QR code from the QR generator.
  • Follow up politely the day an invoice becomes overdue.

Use the generator

The invoice generator does the arithmetic and gives a printable invoice you can save as a PDF; nothing is uploaded. Check tax rules for your country with your accountant or tax authority.

Practice questions

Test yourself, then tap to check. Answers are calculated by the tools linked below.

  1. Add 20% VAT to £450.
    Show answer

    Price including tax (gross): £540.00 · VAT to add: £90.00

  2. A$330 includes 10% GST. How much is the GST?
    Show answer

    Price before tax (net): A$300.00 · GST included: A$30.00

  3. A $64.90 receipt includes 9% sales tax. What was the price before tax?
    Show answer

    Price before tax (net): $59.54 · Sales tax included: $5.36

Frequently asked questions

What must an invoice include?

Seller and buyer details, a unique number, dates, itemised charges, totals with tax and payment instructions. Some countries require a tax registration number.

How do I calculate tax on an invoice?

Multiply the discounted subtotal by the tax rate and add it to get the total.

How long should payment terms be?

14 to 30 days is common; shorter terms get paid faster.

Can I save an invoice as a PDF?

Yes — use print and choose Save as PDF.

Try it yourself

Invoice GeneratorCreate a clean invoice with line items, tax, discount and totals, then print it or save it as a PDF — free, no sign-up.VAT CalculatorAdd VAT to a price, remove VAT from a total or find the VAT rate — with UK 20%, 5% and 0% presets.GST CalculatorAdd or remove GST on a price, with New Zealand 15%, Australia 10% and Canada’s 5% federal rate presets.Sales Tax CalculatorAdd sales tax to a price, take it out of a total, or find the tax rate from two prices.

Keep learning

How to Calculate Sales Tax, VAT and GST6 min readHow to Calculate a Discount5 min readHow to Calculate Percentages7 min read

Reviewed by Thomas M, Registered Investment Adviser (South Carolina), who launched his own financial advisory firm in 2010. Spot a mistake? Tell us. See our editorial policy. Finance content is educational and not financial advice; see the disclaimer.