In terms of formal information, writing an invoice does not differ all that much from writing a proposal, an order confirmation, or even a delivery note. All of these are structured very similarly and require the same information at several stages throughout.
As with any other business letter, the company logo should be of good print quality and clearly visible on the invoice – most are placed in the upper section of the document. If it so happens that you have no logo or you don’t want to use one, you can alternatively place the company name there.
Thereafter follows the usual formalities of a business’ correspondence with a customer, i.e. the name, title, and address of the customer, as well as the appropriate information of the firm. It is also of course advisable to include your own contact details (telephone, e-mail) for future inquiries that might be sent back to you. At this point it is also a possibility to include your tax identificationnumber or GST registration number (depending on which you use for the company). Alternatively, it is possible to list the tax number with additional information, e.g. account information, in the header or the footer.
After the title (usually ‘Invoice’ is sufficient for this) comes the individual portion of the invoice. The customer number and date should be written next to the invoice number. In the brief running text of the letter you should thank the customer for their order and list the products and/or services. Then you note the amount of products (or services) being provided. Using bullet points or abbreviations you can outline the type of product/service, and finally then the corresponding price for each.
If it is the case that you are selling more than one of the same product to a customer, then you should include not just the quantity, but also the individual price alongside the total price.
Once all the individual payments have been listed it is now time to communicate the total amount of the invoice. Next you should list the sum of all the named payments followed by the total amount of GST, which will be added to this net amount. Finally, add these two figures to reveal the final amount of the invoice.
Underneath the gross sum, you should inform the consumer of the date that the payment is due (don‘t forget to include your account details within the invoice) and also stipulate the delivery date as well.