Hi flasher,
I'm involved in international trade and need to do a lot of invoices and such.
May I make a suggestion first on invoice numbers? I use a combination of the date of the invoice, an acronym of the client's company and a number; for example 261002CIF006 so I can tell at a glance when it was sent, to whom and which one to refer the client to if they are 'remiss' in paying. If you are operating under full contract then use the contract number as well - 261002CIFcontract#006
As onpnt noted, if you are charging by the hour then you do need to note the charge and the hours you are charging for on the current invoice. Make the invoice simple but clear, and as detailed as possible so that the client will not have recourse to query you on any point and thus delay payment.
You can easily use Word to make up an invoice:
Do a table form with perhaps three rows and three columns - one small top row for the indications - service//description-this invoice//amount; one large row where you can detail all such as: maintenance @$xx.00 per hour//this billing period=5 hours//$xx.00.
Then a final bottom row showing in the all-important amount column "Total Owing this billing period" $xx.00. Merge the first two cells of the bottom column so you have only two - one large for the text and one small under the amount column.
Above the table of course note your company name (and insert a logo if you have one), write Payment Invoice (you would be surprised how many customers will come back to you if you don't and tell you they did not know that it was a demand for payment invoice but just perhaps a ProForma Invoice (description of services and charges), note the full name and address of the customer in the same way you would on a business letter, the period of this billing period, the invoice number, today's date.
Below the table, note any pertinent payment details such as your bank account - if they are using that method - or whatever, under a heading such as
"Please make payment to ......" and as onpnt mentioned, it is perfectly acceptable and is good business practice to note here the date by which payment is due such as "Please make payment before such and such a date."
And include "For questions regarding this invoice please contact so and so at ..." and include your contact details, and end it with something like "Thank you for your custom" or some such of an idea to let them know you appreciate their service.
Play with the look of the invoice but don't make it too garish and once you have the basic look to your satisfaction save it as .dot template and then you can use it regularly as it is important that the you use the exact same design each time you send an invoice so the client recognizes easily what he is receiving.
I would also suggest that you make at least two invoice templates - one wherein the language used is polite and professional and another wherein you have removed the "Pleases" - but which is still professional. This one should be titled "Payment Now Due" and in all other respects should be identical in design. Replace "Please make payment by..." with "Our records show your account is now due. Remittance of #xx.00 is now required. If you have any questions contact so and so at ....."
You will need sometimes to make such a request as you will have clients that are lax in paying for one reason or another.
HTH