Expert: Arthur Naman - 3/9/2011

Question
I need a formula to compute the interest that should be received on tax certificates when the payment is received.  The interest would be simple interest, usually 18% per year, that is added to the balance of the certificate monthly (payment must be received by the 1st of the month).  The interest only gets computed on the original amount we paid for the certificate and we never know when it will be paid, but it has to be paid within a 2 year period.  For example, we purchase a certificate on 6/1/2010 in the amount of $162.62, payment is received on 12/10/2010.  The interest we received on that amount would be $17.08 (7 months 6/10-12/10).  Is there a  formula I could use on my spreadsheet to give me that amount of expected interest?  Basically I need a formula that will calculate the interest on a montly basis from the original amount invested until it is paid.  

I already posted this question to an Excel expert in the forum and he suggested I ask an accountatn.  Thank you for any assistance you can offer.

Answer
I need to respond this way due to the limits of the AllExperts forum. I need some extra time to work on this; AllExperts does not provide for this. If I take more than a few days AllExperts will drop me from being an expert and I do not want that.

What I need you to do is to provide me with an e-mail address I can use to communicate with your directly.

My e-mail is anaman@naman.com.

This is, in fact, a typical spreadsheet question. I have access to excel and software from Open Office's calc. We can exchange e-mail messages until you get the result you are looking for.

Thanks. p.s. If you are located in or around Austin Texas we can meet.