diff --git a/Makefile b/Makefile
index d54cd5b..4ac9153 100644
--- a/Makefile
+++ b/Makefile
@@ -3,5 +3,5 @@ reference:
 	amortize -P 100000 -r 0.05 -f monthly -n 36 -s > ref.txt
 
 test:
-	python src/amort.py -p 100000 -i 5.0 -t 3 -ot "{\"payment_number\":13,\"amount\":5000}"
+	python src/amort.py -p 100000 -i 5.0 -t 3 -ot "{\"payment-number\":13,\"amount\":5000}"
 
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..9608fad
--- /dev/null
+++ b/README.md
@@ -0,0 +1,45 @@
+
+# amort
+
+Generates an amortization schedule based on the principal, interest rate, term, and any additional payments towards principal.
+
+## requirements
+
+Only imports `argparse` and `json` for the main block of the script.
+
+* saves results to a file `schedule.csv`
+* does not access the web or internet
+
+## usage
+
+Invoke `make test` to generate a schedule based on loan of 100,000 over a 3 year term given an interest rate of 5.0% with a one-time payment towards principal of 5000 at the 13th month.
+
+### extra payments
+
+For extra payments towards principal, invoking the script will look like:
+
+    python src/amort.py -p {principal} -i {interest rate} -t {years} --extra-payments extra_payments.json
+
+A valid json file contains an list named `extra-payments`. Each element is an object with the attributes `payment-number` and `amount`.
+
+    {
+        "extra-payments" : [
+            {
+                "payment-number": 1,
+                "amount": 500
+            }, {
+                "payment-number": 2,
+                "amount": 500
+            }, {
+                "payment-number": 3,
+                "amount": 500
+            }
+        ]
+    }
+
+* `payment-number` is the month when the payment has been made.
+* `amount` is self-explanatory
+
+## misc
+
+This originated from me playing with ChatGPT. I asked it a question and it blurted out a semi-functional script as an answer. Then I made this repo to track the errors I fixed.
diff --git a/src/amort.py b/src/amort.py
index b06a824..1d0db32 100644
--- a/src/amort.py
+++ b/src/amort.py
@@ -27,7 +27,7 @@ def generate_amortization_schedule(principal, interest_rate, loan_term, extra_pa
         principal_payment = round(monthly_payment - interest_payment, 2)
 
         # Apply one-time payment if provided
-        if one_time_payment and payment_number == one_time_payment['payment_number']:
+        if one_time_payment and payment_number == one_time_payment['payment-number']:
             principal_payment += one_time_payment['amount']
             remaining_balance -= one_time_payment['amount']
             if extra_payments != []:
@@ -104,7 +104,7 @@ if __name__ == "__main__":
         p.add_argument("--term", "-t", type=int,\
             help="sets the term (years)")
         p.add_argument("--one-time", "-ot", type=str,\
-            help="factors in a one-time payment (json, example: {\"payment_number\":13,\"amount\":5000}")
+            help="factors in a one-time payment (json, example: {\"payment-number\":13,\"amount\":5000}")
         p.add_argument("--extra-payments", "-ep", type=str,\
             help="facts in multiple one time payments (json file name)")
         args = p.parse_args()
@@ -112,13 +112,12 @@ if __name__ == "__main__":
         if args.extra_payments is not None:
             with open(args.extra_payments) as f:
                 l = json.loads(f.read())
-                # print(extra["extra-payments"])
-        if args.one_time is not None:
-            l.append(json.loads(args.one_time))
         extra = []
         if "extra-payments" in l:
             extra = l["extra-payments"]
-            extra.sort(key=lambda k: k["payment_number"])
+            extra.sort(key=lambda k: k["payment-number"])
+        if args.one_time is not None:
+            extra.append(json.loads(args.one_time))
         return args.principal, args.interest_rate, args.term, extra
 
     principal, interest_rate, loan_term, extra_payments = get_arguments()