loan-calculator

name	loan-calculator
description	Calculate loan payments, amortization schedules, and eligibility estimates for personal loans, auto loans, and mortgages
enabled	true

Instructions

When the user asks about loan payments, how much they can borrow, monthly installments, amortization schedules, or mortgage estimates, use this skill.

1. Quick Payment Calculation

For a simple "What would my monthly payment be?" question, use code_interpreter:

def monthly_payment(principal, annual_rate, term_months):
    """Calculate fixed monthly payment using standard amortization formula."""
    r = annual_rate / 100 / 12  # monthly interest rate
    if r == 0:
        return principal / term_months
    payment = principal * (r * (1 + r)**term_months) / ((1 + r)**term_months - 1)
    return round(payment, 2)

# Example: $250,000 mortgage at 6.625% for 30 years
p = monthly_payment(250000, 6.625, 360)
print(f"Monthly Payment: ${p:,.2f}")
print(f"Total Paid: ${p * 360:,.2f}")
print(f"Total Interest: ${p * 360 - 250000:,.2f}")

2. Full Amortization Schedule

When the user wants a detailed breakdown:

import csv

def amortization_schedule(principal, annual_rate, term_months):
    r = annual_rate / 100 / 12
    payment = principal * (r * (1 + r)**term_months) / ((1 + r)**term_months - 1)
    balance = principal
    schedule = []

    for month in range(1, term_months + 1):
        interest = balance * r
        principal_paid = payment - interest
        balance -= principal_paid
        schedule.append({
            "month": month,
            "payment": round(payment, 2),
            "principal": round(principal_paid, 2),
            "interest": round(interest, 2),
            "balance": round(max(balance, 0), 2),
        })

    return schedule, round(payment, 2)

schedule, pmt = amortization_schedule(250000, 6.625, 360)

# Show first 12 months
print(f"Monthly Payment: ${pmt:,.2f}\n")
print(f"{'Month':>5} {'Payment':>10} {'Principal':>}  ")
( * )
 row  schedule[:]:
    ()


 (, , newline=)  f:
    writer = csv.DictWriter(f, fieldnames=[, , , , ])
    writer.writeheader()
    writer.writerows(schedule)

()

3. Loan Comparison

When the user wants to compare options (e.g., 15-year vs 30-year):

scenarios = [
    {"label": "30-Year Fixed @ 6.625%", "principal": 250000, "rate": 6.625, "months": 360},
    {"label": "15-Year Fixed @ 5.875%", "principal": 250000, "rate": 5.875, "months": 180},
    {"label": "5/1 ARM @ 5.750%", "principal": 250000, "rate": 5.750, "months": 360},
]

print(f"{'Scenario':<30} {'Monthly':>10} {'Total Paid':>12} {'Total Interest':>15}")
print("-" * 70)
for s in scenarios:
    pmt = monthly_payment(s["principal"], s["rate"], s["months"])
    total = pmt * s["months"]
    interest = total - s["principal"]
    print(f"{s['label']:<30} ${pmt:>9,.2f} $ $")

4. Affordability Estimator

When the user asks "How much can I borrow?":

def max_loan(monthly_budget, annual_rate, term_months):
    """Calculate maximum loan principal given a monthly budget."""
    r = annual_rate / 100 / 12
    if r == 0:
        return monthly_budget * term_months
    return monthly_budget * ((1 + r)**term_months - 1) / (r * (1 + r)**term_months)

# Estimate: user can afford $2,000/month, 30-year mortgage at 6.625%
max_amount = max_loan(2000, 6.625, 360)
print(f"Maximum loan amount: ${max_amount:,.2f}")

5. Debt-to-Income Quick Check

For preliminary eligibility:

def dti_check(monthly_income, existing_debts, proposed_payment):
    """Check debt-to-income ratio. Banks typically require DTI < 43%."""
    total_debt = existing_debts + proposed_payment
    dti = total_debt / monthly_income * 100
    status = "Likely Approved" if dti < 36 else "Borderline" if dti < 43 else "May Be Declined"
    return round(dti, 1), status

dti, status = dti_check(
    monthly_income=8000,
    existing_debts=500,   # car payment, student loans, etc.
    proposed_payment=1600  # new mortgage payment
)
print(f"DTI Ratio: {dti}% — {status}")

6. Loan Types Reference

Note: These rates are illustrative defaults from the product-catalog skill. For current rates, check product_catalog first or use web_search.

Loan Type	Typical APR	Terms	Max Amount
Personal Loan	6.99%-17.99%	12-60 months	$50,000
Debt Consolidation	5.99%-15.99%	24-84 months	$100,000
Auto Loan (New)	4.49%-9.99%	36-72 months	$100,000
Auto Loan (Used)	5.49%-11.99%	36-60 months	$75,000
30-Year Fixed Mortgage	6.625%	360 months	Varies
15-Year Fixed Mortgage	5.875%	180 months	Varies
Home Equity (HELOC)	Prime + 0.50%	10-year draw	80% of equity

7. Response Format

Always present results clearly:

• Headline: Monthly payment amount, prominently displayed
• Breakdown: Principal vs. interest per payment
• Totals: Total amount paid and total interest over the life of the loan
• Comparison: If relevant, show alternative scenarios side by side
• Next steps: "Would you like to see the full amortization schedule?" or "Ready to start an application?"

8. Disclaimers

Always include:

"These calculations are estimates for illustrative purposes only. Actual loan terms, rates, and approval are subject to credit review, income verification, and underwriting. Contact a loan officer for a personalized quote."

Chaining

• code_interpreter — runs all financial calculations
• product-catalog — reference current loan product details and rates
• file-sharing — deliver amortization CSVs and comparison exports
• data-analysis — visualize amortization (principal vs interest over time)

Constraints

• All rates shown are illustrative defaults — not live market rates. For current rates, chain with web_search or check product_catalog.
• Never guarantee loan approval
• Never ask for or store SSN, income details, or credit scores in chat
• Always round monetary values to 2 decimal places