Added Amortization Table

financial/amortization_table.py

@@ -0,0 +1,108 @@
+"""
+Program creates an amortization table for a loan, given
+- Principal borrowed
+- Rate of interest per annum
+- Years to repay the loan
+
+Wikipedia Reference: https://www.investopedia.com/terms/a/amortization.asp
+"""
+
+import pandas as pd
+
+
+def payment(principal: float, interest_rate: float, payments: int) -> float:
+    """
+    Calculate the monthly payment for a loan.
+
+    Parameters
+    ----------
+    principal : float
+        The amount of the loan.
+    interest_rate : float
+        The annual interest rate for the loan.
+    years : int
+        The term of the loan in years.
+
+    Returns
+    -------
+    float
+        The monthly payment for the loan.
+
+    Examples
+    --------
+    >>> payment(1000, 0.1, 1)
+    1099.9999999999995
+    """
+    payment = principal * interest_rate / (1 - (1 + interest_rate) ** -payments)
+
+    return payment
+
+
+def amortization_table(
+    principal: float, interest_rate: float, years: int
+) -> pd.DataFrame:
+    """
+    Create an amortization table for a loan.
+
+    Parameters
+    ----------
+    principal : float
+        The amount of the loan.
+    interest_rate : float
+        The annual interest rate for the loan.
+    years : int
+        The term of the loan in years.
+
+    Returns
+    -------
+    pd.DataFrame
+        The amortization table for the loan.
+
+    Examples
+    --------
+    >>> amortization_table(1000, 0.1, 1)
+        Payment  Principal  Interest  Remaining
+    0      0.00       0.00      0.00    1000.00
+    1     87.92      79.58      8.33     920.42
+    2     87.92      80.25      7.67     840.17
+    3     87.92      80.91      7.00     759.26
+    4     87.92      81.59      6.33     677.67
+    5     87.92      82.27      5.65     595.40
+    6     87.92      82.95      4.96     512.45
+    7     87.92      83.65      4.27     428.80
+    8     87.92      84.34      3.57     344.46
+    9     87.92      85.05      2.87     259.41
+    10    87.92      85.75      2.16     173.66
+    11    87.92      86.47      1.45      87.19
+    12    87.92      87.19      0.73       0.00
+    """
+    payments = years * 12
+    interest_rate /= 12
+    payment_amount = payment(principal, interest_rate, payments)
+    amor_table = pd.DataFrame(
+        index=range(payments + 1),
+        columns=["Payment", "Principal", "Interest", "Remaining"],
+        dtype="float",
+        data=0,
+    )
+
+    amor_table["Payment"][1:] = payment_amount
+    amor_table["Remaining"][0] = principal
+    for i in range(1, payments + 1):
+        amor_table["Interest"][i] = amor_table["Remaining"][i - 1] * interest_rate
+        amor_table["Principal"][i] = (
+            amor_table["Payment"][i] - amor_table["Interest"][i]
+        )
+        amor_table["Remaining"][i] = (
+            amor_table["Remaining"][i - 1] - amor_table["Principal"][i]
+        )
+    amor_table = amor_table.round(2)
+    amor_table = amor_table.abs()
+
+    return amor_table
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()