Custom calculations for mortgage rates on form

Question

Working on a PDF form for a client that has a few fillable fields and the rest are auto calculated based off those entries. Calculating the down payment and loan amount based off the purchase price was easy, but I can't figure out the auto calculated APR and P&I based off the rate they input.

This is the formula from an Excel file they gave me for the 30 year P&I (I replaced the cells callouts with what I have the fields labeled—PurchasePrice & ThirtyYearRate).

=PurchasePrice*(((ThirtyYearRate*0.01/12)*(1+(ThirtyYearRate*0.01/12))^360)/((1+ ThirtyYearRate*0.01/12)^360-1))

After I get the P&I figured out, the APR field will be based off the P&I.

I've tried to do some reading online, but Javascript is above me. Any help would be greatly appreciated.

try67 · Answer

JS isn't really that hard. All the operators you used in your formula (except for one) can be used in JS directly to perform calculations.

The only one you need to replace is the power operator ("^"). To do that in JS you need to use the built-in Math.pow command, like so:

2^6 = Math.pow(2,6)

So you just need to access the fields' values, save them into variables, write your formula and at the end apply the result to event.value.

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