ForHosting KIT · Developer Utilities

Car interest calculator

A car interest calculator answers the question auto shoppers, credit unions, and dealer finance desks actually need after the monthly payment: if this vehicle is financed at this annual rate for this many months, how much interest will I pay over the life of the note?

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

The sticker price and the advertised installment hide the true cost of credit. Stretching a used-car loan from thirty-six months to seventy-two months can drop the payment while adding thousands of dollars of finance charges. This tool accepts the three numbers on every auto quote—the loan amount after any down payment or trade-in, the nominal annual rate as a percent, and the term as a positive integer number of months—and returns the total interest cost of a fully amortizing car loan, together with the monthly payment and the total repaid if the schedule runs to maturity. Zero-percent promotional financing is handled as a clean principal split with zero interest, not a divide-by-zero. The same pure module powers the free browser widget and the API path, so a check you run on the landing page matches a script you run later, down to the rounded cent.

How to use it

Enter your values in the form above. The tool checks them before calculating and shows the result on the same page.

Check your inputs

Use the labels and units shown next to each field. If something is missing or outside the allowed range, the page points to the field to fix.

Use it again or automate it

Use the browser tool for individual checks and the API when you need the same capability in an automated workflow.

What you can do with it

Get an answer now

Enter one set of values and see the result without building a spreadsheet or script.

Compare scenarios

Change one value at a time and rerun the calculation to understand what affects the result.

Automate repeated work

Use the API when the same calculation needs to run inside your product or workflow.

FAQ

How do I use this capability?

Complete the fields above and run it on this page. The form highlights anything that needs attention.

For developers — API access

Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.

API endpoint

POSThttps://api.kit.forhosting.com/fin/car-interest

Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.

Call it from your stack

curl -X POST https://api.kit.forhosting.com/fin/car-interest \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"amount":25000,"annual_rate":6.5,"months":60}'

const res = await fetch("https://api.kit.forhosting.com/fin/car-interest", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "amount": 25000,
    "annual_rate": 6.5,
    "months": 60
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/fin/car-interest",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "amount": 25000,
    "annual_rate": 6.5,
    "months": 60
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/fin/car-interest", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"amount":25000,"annual_rate":6.5,"months":60}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"amount":25000,"annual_rate":6.5,"months":60}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/fin/car-interest", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "amount": 25000,
  "annual_rate": 6.5,
  "months": 60
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "fin.car_interest",
  "status": "queued",
  "_links": {
    "result": "/tasks/tsk_…/result"
  }
}

The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.

Pricing

Per request$0.002

Published price — no tokens, no invented credits. A failed task is never charged.

Limits

`max_amount`	1000000000000000
`max_months`	720
`max_rate`	100

Errors

HTTP	Code	Meaning
`401`	`unauthorized`	Missing or invalid API key.
`402`	`insufficient_balance`	Your balance doesn't cover the task price.
`404`	`unknown_type`	That task type doesn't exist.
`429`	`rate_limited`	Too many requests. Use the webhook instead of polling.

Read the full KIT documentation →