@@ -2,42 +2,48 @@
 mortgage.py
 """
 
-PRINCIPAL = 500000.0
-RATE = 0.05
-PAYMENT = 2684.11
-CURRENT_PAYMENT = 0.0
-EXTRA_PAYMENT = 1000.0
-EXTRA_PAYMENT_START_MONTH = 60
-EXTRA_PAYMENT_END_MONTH = 108
-TOTAL_PAID = 0.0
-MONTHS_PAID = 0
+PRINCIPAL: float = 500000.0
+RATE: float = 0.05
+PAYMENT: float = 2684.11
+CURRENT_PAYMENT: float = 0.0
+EXTRA_PAYMENT: float = 1000.0
+EXTRA_PAYMENT_START_MONTH: int = 60
+EXTRA_PAYMENT_END_MONTH: int = 108
+TOTAL_PAID: float = 0.0
+MONTHS_PAID: int = 0
 
-def print_payment_history(months_paid, current_payment, total_payment, principal):
+def print_payment_history(
+    months_paid: int,
+    current_payment: float,
+    total_payment: float,
+    principal: float
+) -> None:
     """
     print_payment_history formats arguments, rounds each argument to two decimals
     and prints themt to the console.
     """
     print(
-        round(months_paid, 2),
+        months_paid,
         round(current_payment, 2),
         round(total_payment, 2),
         round(principal, 2)
     )
 
 while PRINCIPAL > 0:
+    CURRENT_PAYMENT = PAYMENT
     MONTHS_PAID = MONTHS_PAID + 1
 
+    # Make extra payments between months 60 and 108
+    if EXTRA_PAYMENT_START_MONTH <= MONTHS_PAID <= EXTRA_PAYMENT_END_MONTH:
+        CURRENT_PAYMENT = PAYMENT + EXTRA_PAYMENT
+
+    # Last payment should be principal only (no interest) and break out immediately
     if PRINCIPAL < PAYMENT:
         CURRENT_PAYMENT = PRINCIPAL
         TOTAL_PAID = TOTAL_PAID + PRINCIPAL
         PRINCIPAL = 0
         break
 
-    if EXTRA_PAYMENT_START_MONTH <= MONTHS_PAID <= EXTRA_PAYMENT_END_MONTH:
-        CURRENT_PAYMENT = PAYMENT + EXTRA_PAYMENT
-    else:
-        CURRENT_PAYMENT = PAYMENT
-
     TOTAL_PAID = TOTAL_PAID + CURRENT_PAYMENT
     PRINCIPAL = PRINCIPAL * (1 + RATE / 12) - CURRENT_PAYMENT
     print_payment_history(MONTHS_PAID, CURRENT_PAYMENT, TOTAL_PAID, PRINCIPAL)