Loan Calculator API

POST

Calculate monthly loan payments and total interest paid.

Loan Calculator computes monthly loan payments, total interest, and overall loan costs based on principal, annual interest rate, and term length. Include an optional down payment to determine adjusted financing balances and interest ratios.

Try it — live request, no key required

Request

POSTapi.apiverve.com/v1/loanpaymentcalculator

Body

loanAmountnumber

interestRatenumber

loanTerminteger

Verification

Format

No key required to try it. Get a key to use it in your app.

Example

{
  "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": 40961.52,
    "interestRatio": 21.88,
    "formatted": {
      "loanAmount": "$32,000.00",
      "monthlyPayment": "$568.91",
      "totalInterestPaid": "$8,961.40",
      "totalPayment": "$40,961.52"
    },
    "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
      }
    ]
  }
}

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.

What people use it for

Vehicle Financing Calculators: On 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.

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
GraphQL: Query language
MCP: For AI agents

View all integrations →

Other ways to use Loan Calculator

Same data, same APIVerve account, same credit balance — one key works on all of them.

Give it to an AI agentConnect over MCP and your agent calls it as a native tool — Claude, Cursor, ChatGPT.on VerveKit Google Sheets or ExcelA =VERVE() formula fills a column — no script, no export, recalculates in place.on VerveSheets Ground an agent on itA cited, machine-checkable fact your model can't produce on its own.on VerveContext

Questions.

Common questions about the Loan Calculator API.

Read the docs →

How many loan calculations does the Free plan cover?

The Free plan includes 200 credits each month, covering 100 loan calculations at 2 credits per call. For higher volume, the Starter plan covers up to 100,000 calculations monthly, which works out to about $0.30 per 1,000 calls.

Is the month-by-month amortization schedule included on the Free plan?

No, the full amortization schedule is a premium feature reserved for paid plans. Free requests provide the essential calculations like monthly payment and total interest, while any paid plan unlocks the monthly balance breakdown and pre-formatted currency amounts.

Can the calculation account for an upfront down payment?

Yes. You can supply an optional down payment amount with your request. The Loan Calculator subtracts the down payment from the loan amount before calculating interest and monthly payments.

Can I submit loan terms shorter than one year or in months?

No. The loan term parameter requires an integer representing duration in full years, such as 5 for an auto loan or 30 for a mortgage.

Does the calculator accept fractional interest rates?

Yes. The interest rate parameter accepts decimal values, so you can pass specific percentages like 6.875 or 4.25 directly.

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

Parameter	Type	Example	Description
`loanAmount`Required	number	`20000`	The loan amount range 0-inf
`interestRate`Required	number	`5.5`	The interest rate (percentage) range 0-100
`loanTerm`Required	integer	`5`	The loan term in years range 1-50

Optional

Parameter	Type	Example	Description
`downpayment`Optional	number	`5000`	Amount paid up front, subtracted from the loan amount before interest is applied default 0 · range 0-inf

Example request

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}'

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.

Header	When	Value
`x-api-key`Required	Every request	Your API key. Header names are case-insensitive, so `X-API-Key` is the same header.
`Authorization`Alternate	Instead of the above	`Bearer <key>` — for clients that only expose bearer auth. Resolves to the same account and the same billing.
`content-type`Required	POST body	`application/json`

401 is the only auth verdict

A 401 means the key is missing, invalid or expired. A 403 means the key is valid but not permitted here — blocked by a key restriction or an IP allow-list. Running out of credits is a 429.

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.

Sample response

{
  "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": 40961.52,
    "interestRatio": 21.88,
    "formatted": {
      "loanAmount": "$32,000.00",
      "monthlyPayment": "$568.91",
      "totalInterestPaid": "$8,961.40",
      "totalPayment": "$40,961.52"
    },
    "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
      }
    ]
  }
}

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.

Field	Type	Example	Description
`loanAmount`	number	`32000`	Original loan amount in dollars
`downpayment`	number	`0`	Down payment amount applied to loan
`interestRate`	number	`8.5`	Annual interest rate as percentage
`loanTerm`	number	`6`	Loan repayment period in years
`monthly_payment`	number	`568.91`	Required monthly loan payment amount
`total_interest_paid`	number	`8961.4`	Total interest paid over loan term
`total_payment`	number	`40961.52`	Total amount paid over entire loan term
`interestRatio`	number	`21.88`	Percentage of total payment allocated to interest
`formatted`	object	`{...}`	Loan amount and payment totals as dollar strings
`loanAmount`Premium	string	`"$32,000.00"`	Formatted loan amount with currency symbol
`monthlyPayment`Premium	string	`"$568.91"`	Formatted monthly payment with currency symbol
`totalInterestPaid`Premium	string	`"$8,961.40"`	Formatted total interest paid with currency
`totalPayment`Premium	string	`"$40,961.52"`	Formatted total payment amount with currency
`amortization_schedule`Premium	array[3]		Month-by-month breakdown of payments and balances
`month`Premium	number	`1`	Payment period month number
`interest_payment`Premium	number	`226.67`	Interest portion of monthly payment
`principal_payment`Premium	number	`342.24`	Principal portion of monthly payment
`remaining_balance`Premium	number	`31657.76`	Outstanding loan balance after payment

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.

Header	What it carries
`x-api-remaining-credits`	Credits left in the current cycle
`x-api-credits-used`	Credits spent in the current cycle
`x-api-max-credits`	The allowance for the cycle
`x-api-version`	Version of the endpoint that answered

Errors

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

Status	Meaning	What to do
`400`	Input was rejected	Read `error`; it names the parameter that has to change.
`401`	Key missing or invalid	Check the header name and the key value.
`403`	Key valid, but not permitted here	A key restriction or an IP allow-list — never a bad key.
`429`	Rate limited, or out of credits	Read `error` to tell them apart, then back off or top up.

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.

Plan	Per month	Credits	Loan Calculator calls	Per 1,000 calls
Free	Free	200	100	Free
Starter	$29.99	200,000	100,000	$0.30
Pro	$99.99	1,000,000	500,000	$0.20
Mega	$299.99	4,000,000	2,000,000	$0.15

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.

Compare all pricing tiers →

Call it from cURL — POST /v1/loanpaymentcalculator

No SDK to install — this is a plain HTTPS call to /v1/loanpaymentcalculator with your key in the x-api-key header. Swap in a real key and it runs as-is.

cURL

1
2

curl "https://api.apiverve.com/v1/loanpaymentcalculator" \
  -H "x-api-key: YOUR_API_KEY"

Resources

GitHubapiverve/loanpaymentcalculator-apiSource, issues and the examples this page is built from.ReferenceLoan Calculator API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.

Also published for

@apiverve/loanpaymentcalculatornpm APIVerve.API.LoanCalculatorNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from Node.js — POST /v1/loanpaymentcalculator

Install the Node.js SDK, then call the Loan Calculator API with your key. The client wraps the same HTTPS request, so anything it returns is what the endpoint returns.

Install — npm

npm install @apiverve/loanpaymentcalculator

Node.js

const res = await fetch("https://api.apiverve.com/v1/loanpaymentcalculator", {
  headers: { "x-api-key": "YOUR_API_KEY" },
});
const { data } = await res.json();
console.log(data);

Resources

npm@apiverve/loanpaymentcalculatorThe published Node.js client, versioned and signed.GitHubapiverve/loanpaymentcalculator-apiSource, issues and the examples this page is built from.ReferenceLoan Calculator API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.

Also published for

APIVerve.API.LoanCalculatorNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from Python — POST /v1/loanpaymentcalculator

No SDK to install — this is a plain HTTPS call to /v1/loanpaymentcalculator with your key in the x-api-key header. Swap in a real key and it runs as-is.

Python

import requests

res = requests.get(
    "https://api.apiverve.com/v1/loanpaymentcalculator",
    headers={"x-api-key": "YOUR_API_KEY"},
)
print(res.json()["data"])

Resources

Also published for

@apiverve/loanpaymentcalculatornpm APIVerve.API.LoanCalculatorNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from C# / .NET — POST /v1/loanpaymentcalculator

Install the C# / .NET SDK, then call the Loan Calculator API with your key. The client wraps the same HTTPS request, so anything it returns is what the endpoint returns.

Install — NuGet

dotnet add package APIVerve.API.LoanCalculator

C# / .NET

using var client = new HttpClient();
client.DefaultRequestHeaders.Add("x-api-key", "YOUR_API_KEY");

var json = await client.GetStringAsync("https://api.apiverve.com/v1/loanpaymentcalculator");
Console.WriteLine(json);

Resources

NuGetAPIVerve.API.LoanCalculatorThe published C# / .NET client, versioned and signed.GitHubapiverve/loanpaymentcalculator-apiSource, issues and the examples this page is built from.ReferenceLoan Calculator API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.

Also published for

@apiverve/loanpaymentcalculatornpm

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from Go — POST /v1/loanpaymentcalculator

No SDK to install — this is a plain HTTPS call to /v1/loanpaymentcalculator with your key in the x-api-key header. Swap in a real key and it runs as-is.

req, _ := http.NewRequest("GET", "https://api.apiverve.com/v1/loanpaymentcalculator", nil)
req.Header.Set("x-api-key", "YOUR_API_KEY")

res, _ := http.DefaultClient.Do(req)
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
fmt.Println(string(body))

Resources

Also published for

@apiverve/loanpaymentcalculatornpm APIVerve.API.LoanCalculatorNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from PHP — POST /v1/loanpaymentcalculator

No SDK to install — this is a plain HTTPS call to /v1/loanpaymentcalculator with your key in the x-api-key header. Swap in a real key and it runs as-is.

PHP

$ch = curl_init("https://api.apiverve.com/v1/loanpaymentcalculator");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, ["x-api-key: YOUR_API_KEY"]);

$response = curl_exec($ch);
echo $response;

Resources

Also published for

@apiverve/loanpaymentcalculatornpm APIVerve.API.LoanCalculatorNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from Ruby — POST /v1/loanpaymentcalculator

No SDK to install — this is a plain HTTPS call to /v1/loanpaymentcalculator with your key in the x-api-key header. Swap in a real key and it runs as-is.

Ruby

require "net/http"

uri = URI("https://api.apiverve.com/v1/loanpaymentcalculator")
req = Net::HTTP::Get.new(uri)
req["x-api-key"] = "YOUR_API_KEY"

res = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) { |h| h.request(req) }
puts res.body

Resources

Also published for

@apiverve/loanpaymentcalculatornpm APIVerve.API.LoanCalculatorNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

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Loan Calculator API

Try it — live request, no key required

About the Loan Calculator API

What people use it for

Ways to call it

Other ways to use Loan Calculator

Questions.

Request parameters — POST /v1/loanpaymentcalculator

Required

Optional

Authentication

Response — POST /v1/loanpaymentcalculator

Response fields

Response headers

Errors

What a call costs — 2 credits per call

Call it from cURL — POST /v1/loanpaymentcalculator

Resources

Also published for

Call it from Node.js — POST /v1/loanpaymentcalculator

Resources

Also published for

Call it from Python — POST /v1/loanpaymentcalculator

Resources

Also published for

Call it from C# / .NET — POST /v1/loanpaymentcalculator

Resources

Also published for

Call it from Go — POST /v1/loanpaymentcalculator

Resources

Also published for

Call it from PHP — POST /v1/loanpaymentcalculator

Resources

Also published for

Call it from Ruby — POST /v1/loanpaymentcalculator

Resources

Also published for

Zero-code embed — one snippet, no backend

Changelog — Loan Calculator API

Finance

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