This calculator supports two types of mortgages:

Annuity Mortgage: Fixed monthly payments throughout the term

$P = L [c (1 + c) n] / [(1 + c) n - 1]$

Linear Mortgage: Decreasing monthly payments with fixed principal portion

$P / n + P \times r$

P = Monthly Payment
L = Loan Amount
r = Monthly Interest Rate
n = Total Number of Months