Correct....... Unless you have the correct software calculators it's near impossible to get close to an accurate figure.
The initial amount borrowed, the term, the interest rate, duration of the loan, whether there is a residual amount (if commercial lease) all play a part in the final payout figure.
Some institutions may have a payout calculator on their websites but realistically, as the previous poster said, just ring them.
Make sure you have all you loan information in front of you when you do for ID purposes.
Cheers,
Bob.