feat: create get_annuity_due_future_value function

Author: Jeonghyun Min

financial/get_annuity_due_future_value.py

@@ -0,0 +1,56 @@
+"""
+An annuity due means making or requiring payments at the beginning
+of each term during a given period.
+For example, if the given period consists of 3 terms and the payment
+for each term is $1000, then the cash flow is as follows:
+
+    0: $1000 --- 1: $1000 --- 2: $1000 --- 3: no payment
+
+The following function, get_annuity_due_future_value, gives the future value of
+the given annuity due. In the example above, the function should return
+the sum of each payment's future value at the end of term 3.
+
+More info on: https://www.investopedia.com/retirement/calculating-present-and-future-value-of-annuities
+
+This function can help to understand how much you will receive
+if you make a regular deposit for saving with a fix period and interest rate.
+"""
+
+
+def get_annuity_due_future_value(
+    term_payment: float, number_of_payments: int, term_interest_rate: float
+) -> float:
+    """
+    Calculate the future value of the given annuity due
+    :param term_payment: payment made at the beginning of each term
+    :param number_of_payments: the number of payments
+    :param term_interest_rate: the interest rate for each term
+    :return: the future value (maturity value) of the given annuity due
+
+    Examples:
+    >>> round(get_annuity_due_future_value(500, 10, 0.05), 2)
+    6603.39
+    >>> round(get_annuity_due_future_value(1000, 10, 0.05), 2)
+    13206.79
+    >>> round(get_annuity_due_future_value(1000, 10, 0.10), 2)
+    17531.17
+    >>> round(get_annuity_due_future_value(1000, 20, 0.10), 2)
+    63002.5
+    """
+
+    annuity_factor = (
+        ((1 + term_interest_rate) ** number_of_payments) - 1
+    ) / term_interest_rate
+    future_value = term_payment * annuity_factor * (1 + term_interest_rate)
+    return future_value
+
+
+if __name__ == "__main__":
+    user_input_amount = float(input("How much money will be deposited each term?\n> "))
+    user_input_payment_number = int(input("How many payments will be made?\n> "))
+    term_interest_rate = float(input("What is the interest rate per term?\n> "))
+    print(
+        get_annuity_due_future_value(
+            user_input_amount, user_input_payment_number, term_interest_rate
+        )
+    )