1---
2version: 0.1.0
3precision: 2
4form_title: Mortgage Calculator
5form_description: Calculate your monthly mortgage payment. Enter loan amount, interest rate and term to see payment, total interest and amortization schedule.
6form_inputs: Loan amount|loan{€}, Interest rate|rate{%}, Term|term{years}
7form_outputs: Monthly payment|monthly, Total repayment|total, Total interest|interest, First year interest|interest_year1
8---
9# draftply – Mortgage Calculator
10# How much will your mortgage cost per month?
11
12# ── Loan parameters ────────────────────────────────────
13loan = 300000 € # loan amount
14rate = 3.5 % # annual interest rate
15term = 25 years # loan term
16
17# ── Calculations ──────────────────────────────────────
18months = term * 12
19monthly_rate = rate / 12
20
21# Monthly payment (annuity formula)
22monthly = loan * monthly_rate * (1 + monthly_rate)^months / ((1 + monthly_rate)^months - 1)
23
24# Total repayment
25total = monthly * months
26
27# Total interest paid
28interest = total - loan
29
30# Interest in first year
31interest_year1 = loan * rate
32
33# Principal in first year
34principal_year1 = monthly * 12 - interest_year1
35
36# Amortization: remaining principal after each year
37remaining_after_year(n) = loan * (1 + monthly_rate)^(n * 12) - monthly * ((1 + monthly_rate)^(n * 12) - 1) / monthly_rate
38
39# ── Results ─────────────────────────────────────────────
40"Loan amount": loan
41"Interest rate (%)": rate * 100
42"Term": term
43
44"Monthly payment": monthly
45"Total repayment": total
46"Total interest paid": interest
47
48"Interest in year 1": interest_year1
49"Principal paid in year 1": principal_year1
50
51"Remaining after 5 years": remaining_after_year(5)
52"Remaining after 10 years": remaining_after_year(10)
53"Remaining after 15 years": remaining_after_year(15)
54