
1. Re: Need to calculate principal and interest fields on interactive PDF.
try67 Jan 10, 2014 4:31 AM (in response to kevino2)Calculations in Acrobat only kick in when a value is committed, which happens when you leave the field. This can't be changed.
In theory it might be possible to use the keystroke event of a field to change the value of another field, but that is going to be quite complicated and not really worth the trouble, in my opinion.
See this tutorial about setting up advanced calculation in Acrobat: http://acrobatusers.com/tutorials/howtodonotsosimpleformcalculations (although it seems to be offline at the moment)
If you have a specific question after reading this tutorial post a followup here.

2. Re: Need to calculate principal and interest fields on interactive PDF.
George_Johnson Jan 10, 2014 6:10 AM (in response to kevino2)You would normally set all calculated fields to readonly so they are not able to receive the focus and so the user is unable to attempt to change their value. The problem you've having will most likely be fixed if you set the field calculation order (which is not the same as the tab order) to whatever makes sense for the form.

3. Re: Need to calculate principal and interest fields on interactive PDF.
gkaiseril Jan 10, 2014 8:17 AM (in response to kevino2)If you have the outstanding balance before a given payment is made you should be able to compute the amount of interest for that payment. With that amount and the periodic payment amount you can get the amount of principal being paid by subtracting the interest paid for the period from the periodic payment.
It is even possible to create a function that calculates the payment amount with JavaScript in Acrobat and I expect that JavaScript could even compute the Present Value. I used to do this by hand in my college Business Math class.

4. Re: Need to calculate principal and interest fields on interactive PDF.
kevino2 Jan 10, 2014 11:36 AM (in response to gkaiseril)Thanks for the replies and help. Setting the calculated fields to readonly makes a ton of sense, so i will make that change.
What i am looking for is the exact custom calculation script (Javascript) that needs to put on the calculation tab of the Text Field Properties button for one button. This seems like a huge request to me (and perhaps unrealistic), but maybe this is simple for someone who knows Javascript?
The Excel file i'm trying to replicate is here and the button I need calculated is G28.
The new form i've added interactive/calculatable fields to is here and the button I need the Javascript for has a red box around it.
If anyone has time to look at what i've done and offer up any Javascripting help for the button that has the red box around it, i'd be very grateful.

5. Re: Need to calculate principal and interest fields on interactive PDF.
FinancialEngineer Jan 11, 2014 8:22 PM (in response to kevino2)Loan principal may be found using this formula to mimic Excel PV function
PV = FV * (1+RATE)^NPER  PMT * (1+RATE * type) * ( 1 (1+RATE)^NPER ) / RATE

6. Re: Need to calculate principal and interest fields on interactive PDF.
gkaiseril Jan 12, 2014 6:57 AM (in response to FinancialEngineer)You may also need to round the computed values or the breakage or fractional amounts less than 1 cent. If no adjustment is done an error will accumate in the repeated calculations until it becomes obvious.