We've designed this to be as simple as posible to use for you, but without loosing any capabilitie you want to find in a recurrency creation system.
If you want to make an invoice "recurrent", it will be enough for you to set the recurrency period, and set the recurrency option to "yes". The system will then handle all the process, from calculating the next recurrency dates to actually creating the new invoices when they need to be created.
You can define the recurrency period by selecting the time lapse in Years, Months and Days. In most cases, recurrency repetition period will be just "1 month", but if you need to set any other timeframe, you can easily to it by combining years, months and days.
This is how the recurrency tab looks like when you're creating or edition an invoice:
The recurrent bills system is smart, too. Every time that a new invoice is created by recurrency, the "next recurrency date" wil be updated with the next date, calculated automatically by the system. When calculating, it will take care of months with different number of days (30, 31 or 28... even 29) too.
You can manually set the "next recurrency date" if necessary (to "force" a new invoice to be created), but you won't usually need to do that because the system takes care of everything.
New invoices created by recurrency will be created correctly, too: in these new invoices, recurrency will be set to "No" (we want to keep only 1 "mother" invoice!). Also, if there were any payments on the original invoice, they will be included in the new invoice, but they will all be set to "not paid", as you would expect.
The Invoice date will also be setted correctly.
Basically, the new invoice will be identical in everything... except on those things you would expect to not be identical!
If an invoice has Recurrency activated, a little icon will show up in the invoice list so you can quickly see what's the new recurrency date for that invoice, as shown in this screenshot: