Online late interest calculator

Avg Bid (USD)
Project Budget (USD)
$30 - $250

Project Description:
I need programming for a simple Late Interest Rate Calculator. User will be anyone who our accesses website. Website is static. It can use Jquery, JS, PHP, as long as it works.
The following have to be able to be manually changed:
1. Date of payment overdue, preferable input thru a small pop up calendar or (day, month, year, 2 digit for everything) dd/mm/yy format
2. Date of payment (specifics same as the above.
3. Total Invoice value
4. Submit button
5. After pressing submit the following is shown (All in 2 decimals):
- Total owed
-Total debt value (Principal)
-Total interest owed

6. The calculator needs to find applicable interest rate from the table. (Here the late interest rate is adjusted every 6 months and late interests are calculated with different late interest rate for every time range. For example: in 2010 late interest rate is set to 10% and in 2011 late interest rate is 11%. Payment was overdue on 01/01/2010. And it was paid June 1.2011 For whole year of 2010 rate is 10% and then till 1.June it is 11%.
7. I need to be able to access the table and change it when new late interest rate sets in.
8. It needs to be able to use central European languages.
Here is an example of calculator:

If you need further clarification or details please ask before you submit bid.

Thank you for your attention!

Skills required:
Javascript, jQuery / Prototype, PHP, Software Architecture
About the employer:
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