How to write an invoice
A step-by-step guide to writing an invoice that meets legal requirements, without making it harder than it needs to be.
Step 1: Gather the right details
Before you start, you need your own organization or personal number, your VAT registration number (if VAT liable), and the customer's name and address. If you already have this saved in invoicing software, it fills in automatically every time.
Step 2: Add the invoice date and number
Every invoice needs a unique, sequential number, it must never be reused. If you're writing by hand it's easy to lose track, invoicing software always suggests the correct next number automatically.
Step 3: Specify what was sold
Clearly describe the goods or service, and state the quantity and unit price excluding VAT. Add the VAT rate per line, since different items can carry different VAT rates on the same invoice.
Step 4: Calculate the total
Sum the amount excluding VAT, add the VAT amount per rate, and show the total payable. Always double-check the total, rounding errors are the most common cause of incorrect invoices.
Frequently asked questions
Do I have to write the invoice by hand or can I use software?
You can use whatever tool you like, but invoicing software significantly reduces the risk of errors compared to writing manually.
What happens if I forget a mandatory field?
The invoice then fails to meet legal requirements, which can cause problems for both you and the customer when reclaiming VAT.
Can I change an invoice after it's been sent?
No, an issued invoice shouldn't be edited afterwards. If you need to correct something, create a credit note instead.
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