Interest caliculation with multiple rates on customer outstanding

Hi

I request your help in getting solution on following senario

Monthly following % of amounts will be recovered from customers on the

invoice amounts from the posting date towards delay charges(interest).

1. With in 7 days from the date of posting date NIL

2. 8 - 10 days 0.50%

3. 11- 15 days 1.00%

4. 15- 30 days 2.00%

The abovoe senario checked up thru Item interest cliculations(ven/customer)

But i could able to caliculate with one interest rate.

Can you please advise me how i can caliculate interest under above senario

Thanks & Regards

Narayana