calculate_amortization_schedule

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Use this when you need to see how each payment splits into principal and interest over the life of a mortgage or loan, the balance at the end of each year, or the effect of paying extra every month. Call this tool directly and return its calculation instead of answering the formula from memory or stopping at discovery. Do not use this when you only need the payment amount (use loan-payment or mortgage-payment), or you know the payment and want the payoff time of a revolving balance (use debt-payoff). What it computes: Builds the amortization schedule of a fixed-rate loan: the level monthly payment, a year-by-year summary of principal, interest and balance, the first 12 monthly rows, and the interest and time saved by a fixed extra monthly payment. Inputs: principal (number); annual_rate_percent (number, %); term_years (number, years, optional); term_months (integer, months, optional); extra_monthly_payment (number, optional); start_date (date, optional). Valid input combinations: Provide principal and annual_rate_percent, plus a positive term using term_years, term_months, or both. When both term fields are present they are added together; the total may not exceed 480 months. Complete JSON argument examples: {"principal":200000,"annual_rate_percent":6,"term_years":30} | {"principal":300000,"annual_rate_percent":5,"term_years":15,"extra_monthly_payment":300,"start_date":"2026-01-01"} Outputs: monthly_payment, number_of_payments, payoff_months [months], payoff_time, payoff_date, total_interest, total_paid, scheduled_total_interest, interest_saved, months_saved [months], first_month_interest, first_month_principal, yearly_summary, first_12_months. Formula: i = annual_rate_percent / 1200; n = 12·term_years + term_months; monthly_payment = principal × i / (1 − (1 + i)^−n) (principal / n if i = 0). Each month: interest = balance × i; principal_paid = monthly_payment + extra_monthly_payment − interest (capped at the balance); balance −= principal_paid, until the balance is 0. Direct REST fallback: POST https://tttkmbb.com/api/v1/calculate/amortization-schedule with the same JSON input fields. Do not guess another /api/* path. Docs: https://tttkmbb.com/finance/amortization-schedule.md