Give this API a loan amount, an interest rate, and a repayment term, and it returns the ex
Give this API a loan amount, an interest rate, and a repayment term, and it returns the exact monthly payment plus a full month-by-month schedule: interest paid, principal repaid, and balance remaining for every payment. Ask what an extra $300 a month, or a $10,000 lump sum in month 24, would do and it reports the months and interest saved. Every figure uses banker's rounding at pinned precision, so two correct systems agree to the cent. You supply the rate; the API does the math.
10000 (raw units)
price
5
calls / 30d
4
unique payers
2026-09-14
updated
Provider
mortgage-amortization.underscoredone.com · discovered, not yet claimed by its owner
Payment (x402 accepts[])
[
{
"scheme": "exact",
"network": "eip155:8453",
"payTo": "0xE9740820225B3918b4ddd1292C7cA4Ca0e2C2F08",
"asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
"amount": "10000",
"maxTimeoutSeconds": 300
},
{
"scheme": "exact",
"network": "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp",
"payTo": "8ugAWAXDB8V18kiUrGZTq1oMvU3C6Fxs8hfC6rvzQT3b",
"asset": "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v",
"amount": "10000",
"maxTimeoutSeconds": 300
}
]Output schema
{
"bazaar": {
"info": {
"input": {
"body": {
"annual_rate_percent": 6.5,
"extra_monthly_payment": 300,
"one_time_payments": [
{
"amount": 10000,
"month": 24
}
],
"principal": 400000,
"rounding": 2,
"start_date": "2026-07-01",
"summary_only": false,
"term_months": 360
},
"bodyType": "json",
"method": "POST",
"type": "http"
},
"output": {
"example": {
"api_version": "1.0.0",
"inputs_echo": {
"annual_rate_percent": 6.5,
"principal": 400000,
"start_date": "2026-07-01",
"term_months": 360
},
"rounding": {
"decimals": 2,
"final_payment_adjusted": true,
"mode": "half_even"
},
"schedule": [
{
"balance": 399338.4,
"date": "2026-07-01",
"extra_applied": 300,
"interest": 2166.67,
"payment": 2828.27,
"payment_number": 1,
"principal": 661.6,
"scheduled_payment": 2528.27
}
],
"scheduled_payment": 2528.27,
"summary": {
"final_payment": 2530.88,
"payoff_date": "2056-06-01",
"scheduled_term_months": 360,
"total_interest": 510179.81,
"total_paid": 910179.81
},
"with_extra_payments": {
"actual_term_months": 257,
"final_payment": 200.36,
"interest_saved": 175942.33,
"months_saved": 103,
"payoff_date": "2047-11-01",
"total_interest": 334237.48,
"total_paid": 734237.48
}
},
"type": "json"
}
},
"schema": {
"$schema": "https://json-schema.org/draft/2020-12/schema",
"properties": {
"input": {
"additionalProperties": false,
"properties": {
"body": {
"additionalProperties": false,
"properties": {
"annual_rate_percent": {
"description": "Yearly interest rate as a percentage - send 6.5 for 6.5%. Use 0 for an interest-free loan.",
"type": "number"
},
"extra_monthly_payment": {
"description": "Optional extra principal paid every month. Defaults to 0.",
"type": "number"
},
"one_time_payments": {
"description": "Optional lump-sum principal payments; each item needs 'month' and 'amount'.",
"type": "array"
},
"principal": {
"description": "Amount borrowed, in dollars. Must be greater than zero.",
"type": "number"
},
"rounding": {
"description": "Decimal places for money values, 2 to 6. Defaults to 2.",
"type": "integer"
},
"start_date": {
"description": "Date of the first payment, YYYY-MM-DD.",
"type": "string"
},
"summary_only": {
"description": "Set true to return totals only, without the row-by-row schedule.",
"type": "boolean"
},
"term_months": {
"description": "Number of monthly payments. 360 for a 30-year mortgage. Minimum 1.",
"type": "integer"
}
},
"required": [
"principal",
"annual_rate_percent",
"term_months",
"start_date"
],
"type": "object"
},
"bodyType": {
"enum": [
"json",
"form-data",
"text"
],
"type": "string"
},
"method": {
"enum": [
"POST",
"PUT",
"PATCH"
],
"type": "string"
},
"type": {
"const": "http",
"type": "string"
}
},
"required": [
"type",
"method",
"bodyType",
"body"
],
"type": "object"
},
"output": {
"properties": {
"example": {
"properties": {
"api_version": {
"type": "string"
},
"inputs_echo": {
"additionalProperties": true,
"type": "object"
},
"rounding": {
"additionalProperties": true,
"type": "object"
},
"schedule": {
"items": {
"type": "object"
},
"type": "array"
},
"scheduled_payment": {
"type": "number"
},
"summary": {
"additionalProperties": true,
"type": "object"
},
"with_extra_payments": {
"additionalProperties": true,
"type": "object"
}
},
"required": [
"api_version",
"inputs_echo",
"rounding",
"scheduled_payment",
"summary",
"with_extra_payments",
"schedule"
],
"type": "object"
},
"type": {
"type": "string"
}
},
"required": [
"type"
],
"type": "object"
}
},
"required": [
"input"
],
"type": "object"
}
}
}Use it
curl
curl "https://mortgage-amortization.underscoredone.com/calculate" # -> 402 Payment Required, accepts[] lists how to pay # retry with a PAYMENT-SIGNATURE (or PAYMENT header) once paid
JavaScript
const res = await fetch("https://mortgage-amortization.underscoredone.com/calculate");
if (res.status === 402) {
const { accepts } = await res.json();
// pay one of accepts[] via an x402 client, then retry with the payment header
}Python
import httpx
res = httpx.get("https://mortgage-amortization.underscoredone.com/calculate")
if res.status_code == 402:
accepts = res.json()["accepts"]
# pay one of accepts[] via an x402 client, then retry with the payment headerMachine-readable
Everything on this page is also available as clean JSON at /resources/3201.json, and this resource appears in /discovery/resources and /discovery/search.