The invoice number is so both you and the client know what invoice you are talking about if you need to discuss it. Unless the client has already given you a purchase order number or job code to use, you can make up whatever you want - just make sure whatever numbering / coding system you pick, you stick to it!
On my invoices, for example, I use a two letter code for the company, followed by the number of the invoice. So my second invoice to 'John Smith ltd' would have invoice code 'JS2'.
Discuss with an accountant if you have never done this before! Many accountants give their first meeting for free - he can tell you what you need: VAT number, registration as independent etc etc.
pattern and frequency of invoicing normally depends on the nature of projects and varies from one company to the other.
For long-time clients to whom you provide continuous service like maintenance and update, you can send invoice at the end of every month along with timesheet for that month.
For small projects the invoices are sent in two installments: the first one is sent when you sign an agreement and the final one when the project concludes.
For projects that can take months you can devise a milestone based invoicing. The entire project is split into several phases and you send out an invoice upon the completion of each phase. For example, when developing a web application you can mark the completion of a module as a milestone and send out the invoice.
You can use any combination of these to develop an invoicing style that works out the best for you and your client. Mutual agreement , rather than specific methodology, is the key here. Just make sure the client is very clear about when to expect the next invoice.
I use it for my business. It's cheap and has great features like built in stop watch for timing projects and in a single click it will generate a invoice in many different extensions.
Good for client management/time tracking/invoices.
The Vat number is only necessary if you are either a registered company, or earning over 40k or so, in which case you need to be vat registered.
You should also put your UTR number on the invoice also - this is your Unique Tax Reference number which everyone gets. Most companies ask for this, or at least they should do, as without it you can cause them a lot of trouble if you don't declare your invoices to the tax man.
As a note try to avoid over designing your invoices, despite the industry being mainly digital, account departments still print out invoices, so avoid lots of colour and photos etc, it's uses up unnecessary ink. Keep it simple, Its the work that counts.
Justin Atkinson
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Digital Mattepainter / Concept Artist
The Vat number is only necessary if you are either a registered company, or earning over 40k or so, in which case you need to be vat registered.
The amount may change - here it is something like 8k€/year (and also depends on the nature of your work if you need it or not), so check the local tax -fellows about that. ;-)