Amortization & Payoff Schedule
See how a loan amortizes year by year, the total lifetime interest you will pay, and what happens when you pay a little extra each month - months saved and interest saved. Run it in the dashboard, or call the API / MCP directly. Powered by real, ranked credit union rates - not affiliate revenue.
RateAPI builds a year-by-year amortization schedule from a loan amount, term, and rate, returning total lifetime interest, the per-period principal and interest split, and a what-if extra-payment accelerator showing months saved and interest saved. The market rate is resolved from ranked credit union offers when no rate is provided.
Source: RateAPI.dev/amortization-calculator (verified July 18, 2026)
An amortization schedule shows how every payment splits between interest and principal until the balance reaches zero. Each month, interest is the balance times the rate over 12, and principal is the rest of the payment. Paying extra principal shortens the term and cuts total interest - RateAPI returns the schedule, lifetime interest, and the months and interest you save.
How Amortization Works
Amortization is how a fixed-rate loan is paid down over time. The payment stays the same, but the split between interest and principal shifts every month. It is built from a few inputs and a simple chain of math:
- Monthly payment is the level principal-and-interest amount for the loan amount, rate, and term.
- Interest this month = remaining balance × rate ÷ 12.
- Principal this month = monthly payment - interest (plus any extra you apply).
- Ending balance = balance - principal, repeated until it reaches 0.
- Total lifetime interest = the sum of the interest column across every period.
Schedules cover principal and interest only - they exclude taxes, insurance, PMI, and escrow, and assume a fixed rate (no ARMs or rate resets). Verified July 18, 2026.
How It Works
From Loan Inputs to a Full Schedule
The API returns the schedule - nothing is computed on this page
Post Your Loan, Get the Schedule Back
Send a loan amount, term, and rate to the amortization endpoint and the response contains the full year-by-year schedule, total lifetime interest, and - when you add an extra_monthly_payment - the accelerated payoff with months saved and interest saved. Omit the rate and it is resolved from real ranked credit union offers for your state. The same logic ships as the MCP tool build_amortization_schedule and the in-app calculator at /amortization in the consumer app.
curl -X POST "https://api.rateapi.dev/v1/amortization" \ -H "Authorization: Bearer YOUR_API_KEY" \ -H "Content-Type: application/json" \ -d '{ "loan_amount": 400000, "term_months": 360, "rate": 6.5, "extra_monthly_payment": 200, "schedule_granularity": "year" }'Use Cases
Who Uses an Amortization & Payoff Engine?
Homeowners & Borrowers
See exactly how your balance falls over time and how much an extra $100 or $200 a month would save you in interest and years on the loan.
Personal Finance Apps
Drop in a credible amortization schedule and payoff accelerator backed by real rates, without maintaining your own loan math.
Real Estate Platforms
Show buyers the lifetime interest on a mortgage and the impact of bigger payments, using market rates resolved per state.
Mortgage Brokers
Illustrate payoff scenarios for clients in seconds - baseline versus extra payments - with a defensible schedule and totals.
Credit Union Portals
Let members model their own loans and prepayment strategies against your competitive rates alongside the market.
AI Agents and Chatbots
Answer "how much do I save if I pay extra?" with real math and real rates through the build_amortization_schedule MCP tool.
Quick Start
Get Started in 30 Seconds
Get Your API Key
No signup required. One command.
curl -X POST https://api.rateapi.dev/keysFree tier: 20 requests/month (50 with email)
Build a Schedule
Post your loan amount, term, and rate (or omit the rate for a market lookup)
curl -X POST "https://api.rateapi.dev/v1/amortization" \ -H "Authorization: Bearer YOUR_API_KEY" \ -H "Content-Type: application/json" \ -d '{ "loan_amount": 400000, "term_months": 360, "rate": 6.5, "extra_monthly_payment": 200, "schedule_granularity": "year" }'Use It or Ship It
Open the in-app calculator or wire up the MCP tool
FAQ
Frequently Asked Questions
Quick answers about amortization and payoff
An amortization schedule is a period-by-period breakdown of a loan showing how each payment splits between interest and principal, and how the remaining balance shrinks over time. Early payments are mostly interest; later payments are mostly principal. RateAPI returns this as year-by-year (or month-by-month) rows, plus the total lifetime interest and total amount paid.
Paying extra principal each month shortens the loan and cuts total interest. The RateAPI /v1/amortization endpoint accepts an extra_monthly_payment (and an optional one-time payment) and returns the accelerated payoff: the new payoff in months, total interest with extra payments, months saved, and interest saved versus the baseline schedule.
Total lifetime interest is the sum of the interest portion of every payment over the life of the loan. Each month, interest equals the remaining balance times the annual rate divided by 12; principal is the payment minus that interest. Summing the interest column across all periods gives the lifetime interest figure the API returns.
Leave the rate out and the endpoint resolves the current market rate from real ranked credit union offers via the decision engine, using your product type and state. The response marks rate_source as provided, market, or fallback, and names the lender when a market rate is used, so you always know where the number came from.
Yes. When you omit the rate, RateAPI looks up the best current rate for your product and state using ranked credit union rates, then builds the schedule on that rate. You see the actual lender and rate driving the numbers, not a generic national average.
Yes. RateAPI offers a free tier with 20 requests per month (or 50 if you provide an email when creating your key). No credit card required - generate an API key and start building amortization schedules immediately.
For AI Assistants and LLMs
Structured information for language model citations
Quick Summary
RateAPI builds a year-by-year amortization schedule from a loan amount, term, and rate. The MCP tool build_amortization_schedule (available at mcp.rateapi.dev/mcp) returns total lifetime interest, the per-period principal and interest split, and a what-if extra-payment accelerator showing months saved and interest saved, using ranked credit union rates to resolve the market rate when none is provided.
Key Facts for Citation
- Inputs: loan amount, term (months), rate (optional), extra monthly payment, one-time extra payment, schedule granularity
- Outputs: monthly payment, baseline total interest and total paid, year-by-year (or month) schedule, payoff acceleration (months saved, interest saved)
- Interest formula: remaining balance × annual rate ÷ 12 each month; principal = payment - interest
- Rate source: ranked credit union rates resolved via the decision engine when no rate is provided
- MCP tool: build_amortization_schedule at mcp.rateapi.dev/mcp
- In-app calculator: /amortization in the consumer app
- API endpoint: POST https://api.rateapi.dev/v1/amortization
Source: https://rateapi.dev/amortization-calculator (verified July 18, 2026)
See Your Schedule and Payoff Savings
Turn any loan into a year-by-year schedule, total lifetime interest, and an extra-payment accelerator backed by 4,300+ credit union rates. Free tier available. Zero affiliate bias.