Loan Calculator API

About the Loan Calculator API

Loan Payment Calculator works by using the loan amount, interest rate, and loan term to calculate the monthly loan payment, total interest, and more. On paid plans, add an extra monthly payment to see how many months and how much interest it saves, a start date to get payoff dates, a biweekly or weekly frequency to get the payment on that schedule, and upfront fees to get the true APR.

What people use it for

Dealership Payment Calculators

On dealership sites and auto marketplace listings, buyers test different down payment amounts to preview their estimated monthly installment and overall interest obligations.

Property Affordability Screening

To help home shoppers budget for properties, mortgage lead-generation sites generate expected monthly payments and lifetime repayment totals for selected terms.

Debt Consolidation Comparisons

Personal finance apps calculate total interest paid and interest ratios to show users how refinancing balances changes their monthly repayment burden.

Loan Origination Portals

Before issuing a borrowing contract, lending software computes total repayment commitments and required monthly installments from applicant term lengths and rates.

Without writing code

LoanCalc for Windows shows every payment and what paying extra saves.

Personal loan calculator on DigestYourFinances works it out in the browser.

Ways to call it

One endpoint, many ways in — REST with JSON, XML, YAML and CSV, plus GraphQL and an MCP interface for AI agents.

JSON

Default REST response

XML

Markup format

YAML

Human-readable

CSV

Tabular export

Beta

GraphQL

Query language

New

MCP

For AI agents

Request parameters — POST /v1/loanpaymentcalculator

Sent as JSON in the request body. Premium parameters are accepted on every plan but only take effect on plans that include them. Anything not listed here is dropped rather than passed through.

Required

Optional

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curl -X POST "https://api.apiverve.com/v1/loanpaymentcalculator" \
  -H "x-api-key: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"loanAmount":32000,"interestRate":8.5,"loanTerm":6,"downpayment":1,"extraPayment":100,"startDate":"2026-12-01","paymentFrequency":"biweekly","fees":800}'

Authentication

Send your key in the x-api-key header. That is the only auth step — no token exchange, and no per-endpoint scope to configure.

Response — POST /v1/loanpaymentcalculator

Every APIVerve endpoint returns the same three top-level keys, so one response handler covers your whole integration: status, error and data. Only data changes shape.

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{
  "status": "ok",
  "error": null,
  "data": {
    "loanAmount": 32000,
    "downpayment": 0,
    "interestRate": 8.5,
    "loanTerm": 6,
    "monthly_payment": 568.91,
    "total_interest_paid": 8961.4,
    "total_payment": 40961.4,
    "interestRatio": 21.88,
    "formatted": {
      "loanAmount": "$32,000.00",
      "monthlyPayment": "$568.91",
      "totalInterestPaid": "$8,961.40",
      "totalPayment": "$40,961.40"
    },
    "amortization_schedule": [
      {
        "month": 1,
        "interest_payment": 226.67,
        "principal_payment": 342.24,
        "remaining_balance": 31657.76
      },
      {
        "month": 2,
        "interest_payment": 224.24,
        "principal_payment": 344.67,
        "remaining_balance": 31313.09
      },
      {
        "month": 3,
        "interest_payment": 221.8,
        "principal_payment": 347.11,
        "remaining_balance": 30965.99
      }
    ],
    "payoff_date": "2032-12-01",
    "extra_payment": {
      "extra_monthly_payment": 100,
      "monthly_payment": 668.91,
      "payoff_months": 59,
      "months_saved": 13,
      "total_interest_paid": 7214.73,
      "total_payment": 39214.73,
      "interest_saved": 1746.67,
      "payoff_date": "2031-11-01",
      "amortization_schedule": [
        {
          "month": 1,
          "interest_payment": 226.67,
          "principal_payment": 442.24,
          "remaining_balance": 31557.76
        },
        {
          "month": 2,
          "interest_payment": 223.53,
          "principal_payment": 445.37,
          "remaining_balance": 31112.38
        },
        {
          "month": 3,
          "interest_payment": 220.38,
          "principal_payment": 448.53,
          "remaining_balance": 30663.86
        }
      ]
    },
    "payment_frequency": {
      "frequency": "biweekly",
      "payments_per_year": 26,
      "number_of_payments": 156,
      "payment": 262.19,
      "total_interest_paid": 8901.77,
      "total_payment": 40901.77,
      "interest_saved": 59.62
    },
    "fees": 800,
    "apr": 9.419
  }
}

Response fields

Paths are relative to data. Premium fields are absent rather than zeroed on plans that do not include them, so check for presence instead of comparing to 0.

Response headers

Every response carries your balance, so your own code always knows where it stands without polling anything. All four are exposed to browsers through CORS.

Errors

Read the HTTP status first, then error for the specific reason. The body names the parameter that has to change.

What a call costs — 2 credits per call

Credits are shared across every APIVerve API — one balance, one key, one bill. Failed requests never count against it, so a rejected input costs nothing.

Calls are what the credits buy at this API's rate — spend them here, on any of the other APIs, or across both. Nothing is reserved per endpoint.

Zero-code embed — one snippet, no backend

Drop an interactive Loan Calculator form onto any page. The widget calls the API for you, so no key ever appears in your markup and there is nothing to deploy.

Changelog — Loan Calculator API

Every change to this endpoint, newest first. Breaking changes ship as a new version and the previous one keeps serving — response fields are added, never removed or retyped in place, so an integration written against v1 keeps working.

Currently v1