Overdue invoices with mini payments

Hello

I am trying to achieve the following

I have one customer with multiple invoices.
The customer can pay some invoices in full and some invoices with mini payments, until the entire amount has been payed.

I want to start implementing overdue fees to late invoices but have no idea how to calculate these fees for invoices that have mini payments.

Example:

Invoice 1#
Amount: 100 EUR
Issue Date: 14 March 2013
Overdue on: 28 April 2013

1st payment on 15 March 2013: 10 EUR
2nd payment on 29 April: 20 EUR
3rd payment on 10 July: 70 EUR



Invoice 2#
Amount: 200 EUR
Issue Date: 15 March 2013
Overdue on: 29 April 2013

1st payment on 20 March 2013: 100 EUR
2nd payment on 30 April: 100 EUR


How can I calculate overdue fees in this case?

Hello,

you can try sth like this (see attachement)
frirs sheet /invoices/ is just for basic information eg
Invoice number
Amount: 100 EUR
Issue Date: 14 March 2013
Overdue on: 28 April 2013
second sheet is for payments, fill firs 3 columns and copy down the formula from colund D where you can see hah many days the mini payments are overdue
not sure if you like this but may be it could help a bit

greetings

Thank you very much.
I will work and continue on your idea.

All the best