In a couple years, he will probably learn that maintaining this invoice system to support the changes in his business will prove to be a frustrating waste of time.<p>For a reasonable fee, I now use Freshbooks.  I love paying a small fee to have a company constantly improving and perfecting the invoice system I use, and the system saves me A LOT of time each month.<p>13 years ago, I could just put numbers in an invoice in word, send it to a customer, they paid by check.  Then over the years, it got much more complicated.  In-house tools, mixed with other accounting software, was just sucking time.<p>I know it&#x27;s fun to write tools like this for business tasks, but I think you also have to pick your battles, and when you can pay for an affordable tool that will greatly simplify a business task, I choose this path.<p>EDIT: I recently started using Freshbooks&#x27; API to do little reporting tasks they don&#x27;t provide, and this fills the &quot;make my own tools&quot; void when it comes to accounting.