Hi, I'm Robert and I'll be helping you with your financial software question.
what software are you using ?
You can customize the invoices to a point. Changing the headings you certainly can do. I don't know about changing the size of the invoice itself although you can certainly change the size of things on it.
These are two links that show exactly how to customize invoices in quickbooks and are written to be easily understood
This one is from quickbooks and includes a video tutorial that lasts about 3 minutes
Have you looked into issuing statements ? In my experience a lot of psychologists wont hand a patient an invoice every session but rather keep the invoices internal and send a statement of what is owed for the month instead. That has the advantages of
A. not looking like they bought a wrench at the hardware store as I assume is your goal
B. Keeping track of the total owed rather than tracking by each appointment. So if they have 4 appointments at 100 each and pay you 300 at the end of the first month the nexts month's statement would show them owing 500.
can you be more definitive of exactly what you want ?
They are usually designed to fit on a standard letter size paper or an invoice form.
I don't think that you can change that although you can change the headings etc.
what size would you like them ? As most printers print letter size paper standard there is not a lot of call for printing on a smaller piece of paper.
I don't know how you want it so I don't know how possible it is.
The first thing that you should check though is the template forms gallery which unfortunately is not working through the intuit site at the moment but you should be able to find it in quickbooks under forms
there might be a premade form that does exactly what you want it to.
If you want somebody to do it for you onsite quickbooks has certified experts that you can look up by zipcode and speak to any of them until you find one that you think will do what you want for a price that you want