"nytcpa" wrote:
looking for a free online (or template) that can generate a
full amortization schedule when one variable (usually the
interest rate) is unknown.

I think you are trying to say that you know the payment
amount, original (or current) balance of the loan, and the
original (or remaining) term of the loan.

Try taking an Excel template and changing the cells for
interest and payment. Usually the payment cell uses the
PMT(...) function. Replace that with a constant. Usually
the interest cell contains a constant. Replace that with
the following formula:

=12*RATE(months, payment, -balance)

Caveat: If you only have the current balance and remaining
term of the loan in months, you might encounter further
problems if the remaining term is not a multiple of years.
Ideally, work with the original balance and term.
Alternatively, find a template that expresses the term of
the loan in months, not years.