{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"amortization-schedule"},"result":{"entity_type":"calculator","id":"amortization-schedule","calculator_id":"amortization-schedule","canonical_url":"https://tttkmbb.com/finance/amortization-schedule","name":"Amortization Schedule Calculator","title":"Amortization Schedule Calculator – Yearly Summary, First 12 Months and Extra-Payment Savings","category":"finance","category_name":"Finance","tool_name":"calculate_amortization_schedule","featured_mcp_tool":true,"description":"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.","use_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.","do_not_use_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).","inputs":[{"name":"principal","label":"Loan amount","type":"number","required":true,"max":1000000000000,"exclusive_min":0,"description":"Amount borrowed.","example":200000},{"name":"annual_rate_percent","label":"Annual interest rate","type":"number","unit":"%","required":true,"min":0,"max":100,"description":"Fixed nominal annual rate in percent; the monthly rate is this / 12.","example":6},{"name":"term_years","label":"Term (years)","type":"number","unit":"years","required":false,"min":0,"max":40,"description":"Loan term in years; added to term_months when both are given. Total term is limited to 40 years.","example":30},{"name":"term_months","label":"Term (months)","type":"integer","unit":"months","required":false,"default":0,"min":0,"max":480,"description":"Additional months of term (e.g. term_months=60 alone for a five-year loan).","example":0},{"name":"extra_monthly_payment","label":"Extra monthly payment","type":"number","required":false,"default":0,"min":0,"max":1000000000000,"description":"Optional fixed amount paid on top of the scheduled payment every month, applied to principal.","example":0},{"name":"start_date","label":"Loan start date","type":"date","required":false,"description":"Optional loan origination date (YYYY-MM-DD); the first payment is due one month later and payoff_date is reported.","example":"2026-01-01"}],"outputs":[{"name":"monthly_payment","label":"Scheduled monthly payment","type":"number","decimals":2,"description":"Level payment from the annuity formula (before any extra payment)."},{"name":"number_of_payments","label":"Scheduled number of payments","type":"integer","decimals":0,"description":"12 × term_years + term_months."},{"name":"payoff_months","label":"Months to payoff","type":"integer","unit":"months","decimals":0,"description":"Actual number of payments including the extra payment (equals number_of_payments without one)."},{"name":"payoff_time","label":"Payoff time","type":"string","decimals":4,"description":"payoff_months in years and months."},{"name":"payoff_date","label":"Payoff date","type":"date","decimals":4,"description":"start_date plus payoff_months (only when start_date is given)."},{"name":"total_interest","label":"Total interest","type":"number","decimals":2,"description":"Interest paid over the actual schedule (with extra payments)."},{"name":"total_paid","label":"Total paid","type":"number","decimals":2,"description":"principal + total_interest."},{"name":"scheduled_total_interest","label":"Interest without extra payments","type":"number","decimals":2,"description":"monthly_payment × number_of_payments − principal."},{"name":"interest_saved","label":"Interest saved by extra payments","type":"number","decimals":2,"description":"scheduled_total_interest − total_interest."},{"name":"months_saved","label":"Months saved","type":"integer","unit":"months","decimals":0,"description":"number_of_payments − payoff_months."},{"name":"first_month_interest","label":"Interest in the first payment","type":"number","decimals":2,"description":"principal × annual_rate_percent / 1200."},{"name":"first_month_principal","label":"Principal in the first payment","type":"number","decimals":2,"description":"monthly_payment + extra_monthly_payment − first_month_interest."},{"name":"yearly_summary","label":"Yearly summary","type":"list","decimals":2,"description":"One row per loan year: year, principal_paid, interest_paid, ending_balance (at most 40 rows)."},{"name":"first_12_months","label":"First 12 months","type":"list","decimals":2,"description":"Rows for months 1–12: month, payment, principal, interest, balance."}],"input_schema":{"type":"object","properties":{"principal":{"description":"Amount borrowed.","type":"number","maximum":1000000000000,"exclusiveMinimum":0,"examples":[200000]},"annual_rate_percent":{"description":"Fixed nominal annual rate in percent; the monthly rate is this / 12. Unit: %.","type":"number","minimum":0,"maximum":100,"examples":[6],"x-unit":"%"},"term_years":{"description":"Loan term in years; added to term_months when both are given. Total term is limited to 40 years. Unit: years.","type":"number","minimum":0,"maximum":40,"examples":[30],"x-unit":"years"},"term_months":{"description":"Additional months of term (e.g. term_months=60 alone for a five-year loan). Unit: months.","type":"integer","minimum":0,"maximum":480,"default":0,"examples":[0],"x-unit":"months"},"extra_monthly_payment":{"description":"Optional fixed amount paid on top of the scheduled payment every month, applied to principal.","type":"number","minimum":0,"maximum":1000000000000,"default":0,"examples":[0]},"start_date":{"description":"Optional loan origination date (YYYY-MM-DD); the first payment is due one month later and payoff_date is reported.","type":"string","format":"date","examples":["2026-01-01"]}},"additionalProperties":false,"required":["principal","annual_rate_percent"]},"output_schema":{"type":"object","properties":{"monthly_payment":{"description":"Level payment from the annuity formula (before any extra payment).","type":"number"},"number_of_payments":{"description":"12 × term_years + term_months.","type":"integer"},"payoff_months":{"description":"Actual number of payments including the extra payment (equals number_of_payments without one). Unit: months.","type":"integer","x-unit":"months"},"payoff_time":{"description":"payoff_months in years and months.","type":"string"},"payoff_date":{"description":"start_date plus payoff_months (only when start_date is given).","type":"string","format":"date"},"total_interest":{"description":"Interest paid over the actual schedule (with extra payments).","type":"number"},"total_paid":{"description":"principal + total_interest.","type":"number"},"scheduled_total_interest":{"description":"monthly_payment × number_of_payments − principal.","type":"number"},"interest_saved":{"description":"scheduled_total_interest − total_interest.","type":"number"},"months_saved":{"description":"number_of_payments − payoff_months. Unit: months.","type":"integer","x-unit":"months"},"first_month_interest":{"description":"principal × annual_rate_percent / 1200.","type":"number"},"first_month_principal":{"description":"monthly_payment + extra_monthly_payment − first_month_interest.","type":"number"},"yearly_summary":{"description":"One row per loan year: year, principal_paid, interest_paid, ending_balance (at most 40 rows).","type":"array"},"first_12_months":{"description":"Rows for months 1–12: month, payment, principal, interest, balance.","type":"array"}}},"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.","method":"Standard monthly amortization with end-of-month payments and the extra amount applied to principal from the first month; the final payment is reduced to what remains. Lenders round payments to cents, so real schedules can differ by a few cents.","sources":[{"name":"Wikipedia – Amortization calculator (annuity payment formula)","url":"https://en.wikipedia.org/wiki/Amortization_calculator","type":"reference","retrieved_at":"2026-09-24"},{"name":"Investopedia – Amortization Schedule: Definition, Formula and Example","url":"https://www.investopedia.com/terms/a/amortization_schedule.asp","type":"reference","retrieved_at":"2026-09-24"},{"name":"CFPB – Owning a Home: loan costs and monthly payment components","url":"https://www.consumerfinance.gov/owning-a-home/","type":"government","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"200,000 at 6 % for 30 years","inputs":{"principal":200000,"annual_rate_percent":6,"term_years":30},"expected":{"monthly_payment":1199.1,"number_of_payments":360,"payoff_months":360,"payoff_time":"30 years","total_interest":231676.38,"total_paid":431676.38,"scheduled_total_interest":231676.38,"interest_saved":0,"months_saved":0,"first_month_interest":1000,"first_month_principal":199.1},"url":"https://tttkmbb.com/api/v1/calculate/amortization-schedule?principal=200000&annual_rate_percent=6&term_years=30"},{"name":"300,000 at 5 % for 15 years with 300 extra per month from 2026-01-01","inputs":{"principal":300000,"annual_rate_percent":5,"term_years":15,"extra_monthly_payment":300,"start_date":"2026-01-01"},"expected":{"monthly_payment":2372.38,"number_of_payments":180,"payoff_months":152,"payoff_time":"12 years 8 months","payoff_date":"2038-09-01","total_interest":105316.26,"scheduled_total_interest":127028.56,"interest_saved":21712.3,"months_saved":28},"url":"https://tttkmbb.com/api/v1/calculate/amortization-schedule?principal=300000&annual_rate_percent=5&term_years=15&extra_monthly_payment=300&start_date=2026-01-01"}],"faq":[{"q":"Why is the first payment mostly interest?","a":"Interest is charged on the outstanding balance, which is largest at the start: 200,000 × 6 % / 12 = 1,000 of the first 1,199.10 payment is interest and only 199.10 reduces the balance. The split reverses as the balance falls."},{"q":"How is the extra payment applied?","a":"It is added to every scheduled payment and goes entirely to principal, which shortens the term and lowers total interest; the scheduled payment itself does not change."},{"q":"Why only a yearly summary and 12 months?","a":"A 30-year loan has 360 rows; the yearly totals plus the first year give the shape of the schedule. Any single month's balance follows from balance = P(1+i)^k − PMT((1+i)^k − 1)/i."}],"tags":["amortization schedule","amortization table","principal and interest breakdown","extra payments","loan payoff","mortgage schedule"],"related":[{"calculator_id":"loan-payment","reason":"Payment and totals without the schedule."},{"calculator_id":"mortgage-payment","reason":"Full housing payment including taxes and insurance."},{"calculator_id":"debt-payoff","reason":"Payoff time for a chosen payment on a revolving balance."}],"links":{"html":"https://tttkmbb.com/finance/amortization-schedule","markdown":"https://tttkmbb.com/finance/amortization-schedule.md","json":"https://tttkmbb.com/finance/amortization-schedule.json","api":"https://tttkmbb.com/api/v1/calculate/amortization-schedule","schema":"https://tttkmbb.com/api/v1/calculators/amortization-schedule","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T01:45:41Z"}